home workshop guns for defense and resistance, vol. v: the ...€¦ · home workshop guns for...
TRANSCRIPT
HOMEWORKSHOP
GUNSfor DefenseandResistance
Volume V
The AR-15/ M16
This page intentionally left blank.
HOMEWORKSHOP
GUNSfor DefenseandResistance
Volume V
The AR-15/ M16
PALADIN PRESS • BOULDER, COLORADO
B i l l H o lm e s
Home Workshop Guns for Defense and Resistance, Vol. V: The AR-15/M16by Bill Holmes
Copyright © 1997 by Bill Holmes
ISBN 13: 978-0-87364-948-3Printed in the United States of America
Published by Paladin Press, a division ofPaladin Enterprises, Inc.,P.O. Box 1307Boulder, Colorado 80306 USA+1.303.443.7250
Direct inquiries and/or orders to the above address.
PALADIN, PALADIN PRESS, and the “horse head” design are trademarksbelonging to Paladin Enterprises and registered in United States Patent andTrademark Office.
All rights reserved. Except for use in a review, no portion of this book may bereproduced, stored in or introduced into a retrieval system, or transmitted in any formwithout the express written permission of the publisher. The scanning, uploading anddistribution of this book by the Internet or any other means without the permission ofthe publisher is illegal and punishable by law. Please respect the author’s rights anddo not participate in the any form of electronic piracy of copyrighted material.
Neither the author nor the publisher assumes any responsibility for the use or misuseof information contained in this book.
Visit our website at www.paladin-press.com.
Also by Bill Holmes:.50-Caliber Rifle Construction Manual: With Easy-to-Follow Full-Scale DrawingsHome Workshop .50-Caliber Sniper Rifle (video)Home Workshop Guns for Defense and Resistance, Vol. I: The Submachine GunHome Workshop Guns for Defense and Resistance, Vol. II: The HandgunHome Workshop Guns for Defense and Resistance, Vol. III:The .22 Machine PistolHome Workshop Guns for Defense and Resistance, Vol. IV: The 9mm Machine PistolHome Workshop Prototype Firearms: How to Design, Build, and Sell Your Own Small ArmsA Master Gunmaker's Guide to Building Bolt-Action Rifles
v
Materials and Tools • 1
Upper Receiver • 9
Bolt • 17
Barrel • 25
Barrel Shroud, Stock, and Grip • 31
Sights • 41
Lower Receiver • 51
Magazines • 73
Small Parts • 83
Fitting and Assembly • 95
Heat-Treating and Finishing • 99
Firing and Adjusting • 103
(TABLE OF
CONTENTS
Although at the time this book was written it was perfectly legal for an individual to manufacture afirearm for personal use, experimental purposes, or research and development, it is likely that new lawshave been added since. It is probably still legal for the upper receiver assemblies described in this book tobe built and assembled on an existing lower receiver. However, if the lower receiver, as described herein,is used, an illegal firearm will result. It is the reader’s obligation to carefully research all pertinent lawsbefore any such construction is attempted.
Technical data presented here, particularly data on ammunition and on the construction, use,adjustment, and alteration of firearms, inevitably reflects the author’s individual beliefs and experienceswith particular firearms, equipment, and components under specific circumstances that the readercannot duplicate exactly. The information in this book should therefore be used for guidance only andapproached with great caution. Neither the author, publisher, nor distributors assume any responsibilityfor the use or misuse of information contained in this book. This book is presented for academic study only.
WARNING
vii
If my memory serves me correctly, it was inearly 1980 that someone suggested to me that a9mm conversion unit to mate with and mount onan AR-15 or M16 lower receiver assembly wouldbe desirable. A bit of research on my partindicated that there was indeed a market for sucha conversion.
At the time I thought it best to use squaretubing for the upper receiver since it was possibleto get more weight into a square bolt of themaximum permissible length than a round one. Abushing was welded into the front end of thereceiver tube and bored and threaded to accept aremovable barrel. This was held in place by abarrel-retaining nut that screwed on to the barrelbushing against the flanged barrel, holding it
securely in place. This same method is used onthe version described in this book.
I made up a magazine adaptor, which notonly reduced the size of the magazine well tojust accept a 9mm magazine (I used Stenmagazines) but also served as a mountingbracket for the ejector and housed the magazinelatch. A combination carrying handle and rearsight assembly was formed from sheet metaland welded in place to match a surplus M16front sight assembly obtained from one of thesurplus military parts companies that flourishedat the time.
After some slight modifications andadjustments the assembled rifle, or carbine as
9mm pistol version. Made in the early 1980s. Rifle version with folding stock from same period.
(PREFACE
viii
HOME WORKSHOP GUNS FOR DEFENSE AND RESISTANCE, VOL. V: THE AR-15/M16
some would call it, performed quite well (wellenough, in fact, that I managed to sell one toalmost everyone who tried it). These were madein both 9mm and .45 caliber.
Since the bolt and recoil springs werecompletely housed in the upper receiver ratherthan extending back into the buttstock as theoriginal parts did, these units were adaptable tofolding stocks as well as pistol versions.
At that time there were several companiesmanufacturing lower receivers for these guns.These were intended, asnow, to be used withmilitary surplus parts toassemble AR-15 or M16rifles. They ranged fromexcellent quality to purejunk. One such gun, whichwas equipped with a castaluminum receiver, wasaccidentally knocked overonto the floor from aleaning position againstthe wall and broke into twoparts. Naturally, I didn’tuse any more of these orinstall my parts on them.In addition, I soondiscovered that dimen sionsvaried considerablybetween the variousbrands—especially themagazine openings.
This did not actuallypresent a problem as longas I was dealing with lowerassemblies belonging tolocal customers. Theybrought them to my shopand I assembled the units,fitting the parts asrequired. The only troubleI experienced was with onewould-be customer. Thispunk was a native of NewYork City, come down toour part of the country toenlighten us poor, ignorant
hillbillies as to how the outside world behaved.He was one of these people who talked all thetime, and when he did let anyone else get in a fewwords he didn’t hear anything they said since hismind was occupied with what he was going to saynext. This guy bought several of these units fromme and ruined every one of them. In spite of whatI told him to the contrary, he tried everything hecould think of to modify them to fire fullautomatic and otherwise “improve” them. I finallygot all I could stand of him and ran him off. He
Full-length view showing unit mounted on Colt-made lower.
Mounted on shop-made receiver.
ix
PREFACE
has ruined almost everyother gun he has owned.
Finally, after the localmarket was satisfied, Idecided to advertise theupper receiver assembliesalong with a magazineadaptor and magazine inseveral national publi -cations. A couple of gunmagazines gave them fav -orable mention, and itwasn’t long before a steadymarket was created.
About this time,though, I made a seriousmistake. I neglected totake into consideration thefact that my averagecustomer didn’t bother toread my instruction sheet.I had built the magazineadaptors to fit the largestmagazine wells I hadencountered, and theinstruction sheet that wasenclosed with each unitdirected the customer toreduce the width of theadaptor slightly until it wasa push fit in the magazineopening, as required. I alsosupplied recoil springs thatwere slightly longer thanneeded, specifying thatthese should be cut, onecoil at a time, untilsatisfactory functioningwas obtained. Theinstructions also explainedthat the rear mounting pinhole sometimes requiredmoving slightly.
Shortly after I beganfilling orders for these Igot a phone call from aman in Florida. Withoutpreamble he proceeded to
9mm conversion unit mounted on commercial receiver.
Same unit on shop-made lower receiver.
x
THE AR-15/M16
call me every foul name he could think of,eventually telling me that the unit I sent himwasn’t worth a damn. When I finally managed toget in a word, I asked him if he had read theinstruction sheet.
“To hell with any instruction sheet,” heretorted. “I’m a federally licensed gunsmith, and Idon’t need an instruction sheet. The damn partsdon’t fit.”
About this time I lost my temper too, and Iproceeded to inform him that possession of afederal firearms license was not an indication ofeither intelligence or ability. I told him that mostof the names he had called me not only applied tohim too, but his mother and wife as well. This got
his attention, so I told him I would send alonganother, slightly smaller magazine adaptor andanother instruction sheet, which I insisted heread. To his credit, several days later I received aletter from him stating that he had made it workand apologizing for his previous conduct.
But such incidents happened too often. Ittook too much time to straighten out theproblems, which were not my fault in the firstplace. I turned the entire operation over to afriend of mine and went on to other things.
Several years later I designed and built a fewof the round-receivered versions similar to thosedescribed in this book. These were made in both9mm and .45 versions and included the open-bolt
9mm conversion (pistol version).
xi
PREFACE
pistol version described herein. This open-boltversion has interchangeable trigger parts thatpivot on the same cross pins as the original partsand will fire both as a full- or semiautomatic. Imade and sold several of these, but after a time—even though I was only furnishing parts—Ibecame concerned about their legality anddiscontinued them as well.
Several months ago, as I prepared to put thisbook together, I built a new upper receiverassembly and a magazine adaptor in the rifleversion that used the standard lower receiverassembly. I also built a new open-bolt pistolassembly using my own parts in the triggermechanism as before. These were fabricatedprimarily for photographic purposes, to use inillustrating this book. These parts includedseveral slight improvements (?) over the olderversions and functioned quite well when attachedto a standard lower receiver.
Then, just about the time I was putting thefinishing touches on the book, another setbackoccurred. Congress passed the so-called “CrimeBill” of 1994, and suddenly lower receivers,which had been selling for $60 to $80 each,skyrocketed to an asking price of more than $400.Even worse, no more can be produced.
Realizing the problem this would cause if thetime ever came when one was compelled to buildsuch a gun or remain defenseless, I went backand designed and built a substitute lower that is
made using formed sheet metal with welded-ingussets and ends. The result is actually quite a bitsturdier than the original, although heavier. Itdoes, however, provide an alternative that willallow the builder to construct the entire gun fromraw materials.
The gun, then, as described in this book, canbe built as either a rifle or pistol, open or closedbolt, semi- or full automatic, and with either aself-contained bolt and recoil spring assembly or aheavier bolt that uses the original recoilspring/buffer assembly.
As things stand at present, it is likely that anyversion of this gun would be illegal if manu -factured in its entirety. However, if the closed-boltversion of the upper receiver assembly is usedwith an existing lower receiver, it would probablybe considered a legal gun. Just how this makeseither version any more or less lethal anddangerous than the other is beyond me. But thedimwits we pay to dream up such rules seem tothink that those laws will, in some fashion,reduce crime.
It is strongly recommended that readerscarefully research all laws concerning building orpossessing such a firearm before finishing andassembling the gun. Unfinished parts are notsupposed to be illegal, but this too may change.Be careful.
This page intentionally left blank.
1
Sheet metal, as used in this project, canusually be obtained locally. The 12-gauge materialcan, as a rule, be found in sheet metal shops andmetal fabrication plants. If possible, try to get thetype with a cold finish, commonly known as “coldrolled.” This will have a bright finish as opposedto the rough black finish of the “hot rolled’’ type.It will cost a little more, but the time saved infinishing it will make up for it. Salvage yards arealso a good source for this. If you aren’t able toobtain it elsewhere, material cut from olderautomobile or light truck frames can be used. Thebiggest problem with this source is the amount of
work it takes to get it. Actually, though, this couldbe an advantage, since the car frame containsbetter material than common sheet metal.
Leaf springs from cars or light trucks can beused for flat stock material, and axles from thesame source will provide round stock. Valvestems salvaged from four-cycle engines, as wellas shock absorber shafts, can be used for small-diameter parts. Most of this material will requireannealing to soften it to a point where it can bemachined easily. This can be done using a largewood fire as described in several of my otherbooks. If a bluing setup is available, material can
(MATERIALSAND TOOLS
A heavy vise can be used as a press brake to form sheetmetal parts, among other uses.
A metal-cutting band saw will save a lot of elbow grease.
2
THE AR-15/M16
be suspended over a bluing tank burner andheated. Actually the term “annealed” is amisnomer as used here, since the hardenedmaterial can be made workable by heating it to atemperature of 800 to 1,000 degrees and allowingit to cool slowly.
4130 seamless tubing, as used here, can beordered from the following supplier:
Wicks Aircraft Supply410 Pine St.Highland, IL 62249
This is the best source of supply for not onlythe tubing but also 4130 and 4340 round stock,as well as flat stock of thesame material. Not onlyare they a source for all ofthe heat-treatable steelrequired, but these arenice people. Anyone whohas dealt with large,arrogant steel companieswho don’t really want todeal in small amounts ofmaterial anyway willappreciate this. Anotherplus is that they will shipby UPS, COD, usuallywithin 24 hours of thetime the order is received.
Leaf springs are the source of heat-treatable flat stock.
Coil springs are available from automotive supply housesand hardware stores.
3
MATERIALS AND TOOLS
Material to be softened is placed in wood pile.
Wood fire will soften hard steel, making it workable.
Softened steel is removed from ashes after cooling.
4
THE AR-15/M16
Sten magazines are still available at areasonable price from the following source:
Manchester ArmsP.O. Box 129Lenoir City, TN 37771
Even before the assault weapons bill wentinto effect, most suppliers of these and othersurplus parts raised their prices to exorbitantlevels with the mistaken idea that there would besuch a demand for these that customers wouldpay the price. The owner of Manchester Arms,told me recently that she still has some 10,000Sten magazines on hand. Her price is $4 each fornew magazines and $2 each for used. You mightwant to order a magazine loading tool at the sametime. These make loading the magazinesconsiderably easier.
Barrel blanks are available from a number ofsources. Most are satisfactory. For some 20 yearsnow I have obtained most of my barrels from thefollowing supplier:
E. R. ShawThoms Run Road and PresleyBridgeville, PA 15017These barrels are fully as good as most that I
have had experience with and far better thansome. And, like most people I deal with a secondtime, the folks at E.R. Shaw are decent, helpfulpeople (unlike some of the arrogant smart alecksat some of the other companies, who seem to feelthat they are doing you a favor if they condescendto sell you something).
Small parts, such as the M1 carbine recoilsprings, hammer springs, hammers, triggers,firing pins, and so on, are available from thefollowing source:
Quality Parts Co.P.O. Box 1479Roosevelt Trail #3Windham, ME 04062
The people at Quality Parts also build theBushmaster versions of the M16 and have builtand sold complete firearms to the military. Theirparts, like their complete guns, are top quality.They sell only new parts, but usually for lessmoney than most of the salvage shysters want forworn out junk.
Round stock is available from many sources.
5
MATERIALS AND TOOLS
Chamber reamers are available from thefollowing source:
Clymer Mfg. Co.1645 W. Hamlin RoadRochester Hills, MI 48309
Here again, I have used these chamber reamersever since the company has been in business, andeven before when it was owned by other people.There are none better for our purpose.
No doubt there are other suppliers whoprovide equal quality, courtesy, and dependability.My endorsement of those listed here is notintended as a slight to anyone else. (Well, almostanyone else.) My experience with those listed hasbeen satisfying enough that I simply neverbothered to look anywhere else.
Several of my other books include fairlythorough discussions of tools and equipment, andthey need not be repeated here. This projectrequires some lathe and mill work, as well as asmall amount of welding. The rest can be donewith hand tools if absolutely necessary.
A lathe is required to build this gun. This welder is capable of MIG, TIG, and stick weldingmodes.
A milling machine will save a lot of hand work, althoughmost operations required here can be done using files,saws, chisels, and grinder.
6
THE AR-15/M16
This gas welding set is used for silver-soldering, heat-treating, and coloring operations.
A large (3/4 to 1 hp) electric motor equipped with an arborcan drive buffing wheels, sanding discs, etc.
Several measuring tools will come in handy.
Welds are dressed flush with the surface.
Various openings are formed as required.
7
MATERIALS AND TOOLS
I have learned recently that several differentmachine tool importers are presently marketing afairly compact combination lathe, millingmachine, and drill press. While most of these areapparently made in the same place and have acommon design with different brand namesaffixed, the best appears to be one called a“Smithy.” This is primarily because it has a holethrough the spindle that is quite a bit larger thanthe others. This will allow the would-be gunbuilder to chuck the barrel and chamber andthread them up close to the head stock with thebulk of the barrel extending through the spindle.This brand also has a longer cross slide (which
does double duty as a milling table) than theother brands I have seen. One of thesemachines—if they are any good—would berelatively inexpensive and require only a smallamount of space. I intend to obtain one in thenear future for use in preparation of a book onhome workshop survival weapons. Stay tuned.
Please note that the suppliers listed herewere in business at the addresses listed whenthis book was published, and since they are allstable companies, I assume that they still are.Please don’t complain to me or the publisher ifthis has changed.
Older horizontal/vertical milling machines can often beobtained quite cheaply. Most are still accurate and offergood value.
Small high-speed grinders will do many of the millingmachine operations.
This page intentionally left blank.
9
The upper receiver, being essentially the samefor both the rifle and pistol versions, is made from1 1/2-inch-outside-diameter seamless tubing witha wall thickness of .120 inch. This is a standardsize, available from most metal supply houses. Itcan also be obtained from aircraft buildingmaterials suppliers, several of which cater tobuilders of home-built aircraft. These areprobably better sources, since they will usuallysell it in short lengths, whereas the metal supplyhouses want to sell full-length sticks measuring20 feet or more.
High strength is not a requirement for the
material used in this receiver since little stress ispresent in use. Although cheaper grades of tubingare available, I would still use the tubing made of4130 if possible. It is tougher than the cheapergrades and will resist wear better. It is also moresuitable for welding than the cheaper grades.
Construction is begun by cutting thereceiver body to length and squaring both ends.Four 1/4-inch or slightly larger holes are drilledjust behind the front face and spaced equallyaround the circumference of the receiver. Aplug, which will serve as a barrel bushing, isturned to a diameter that will just slip into the
(UPPER RECEIVER
Upper receiver ready for polishing (right side). Upper receiver (left side).
10
FOU
R .2
50
” DIA
ME
TER
HO
LES
DR
ILLED
EQ
UA
DIS
TAN
TLY AR
OU
ND
CIR
CU
MFE
RE
NC
E O
FR
EC
EIVE
R. B
AR
RE
L BU
SH
ING
IS W
ELD
ED
INP
LAC
E TH
RO
UG
H TH
ES
E.
BA
RR
EL B
US
HIN
G 1
.10
0”
LON
G. TU
RN
ED
TO C
LOS
E FIT
INS
IDE
RE
CE
IVER
.
LEFT S
IDE
.26
0”
3.0
0”
2.3
00
”3.0
0”.5
00
”.5
25
”
.37
5” D
IA.
UP
PE
R R
EC
EIV
ER
Diagram #1
11
1.5
00
”1
.0”
.50
0”
2.0
”.2
00
”
1.2
50
” .55
0”
BO
TTO
M
RIG
HT
SID
E
UP
PE
R R
EC
EIV
ER
1.6
25
”.8
50
”
7.5
00
”
.60
0”
.50
0”
.87
5”
1.1
25
”
1.5
00
”1
.40
0”
.32
5”
.50
0”
.80
0”
.45
0”
THR
EA
D 1
.12
5”
x 2
4
Diagram #2
12
THE AR-15/M16
front end of the receiver. One-and-a-quarter-inch material is slightly small for this since theinside of the receiver measures 1.260 inches. Soslightly larger material should be turned to fit.While the hole through the bushing will have afinished diameter of .875 inch, it should be keptsmaller and bored to size after the bushing iswelded in place. The bushing should bepositioned inside the receiver with .600 inchextending back into the receiver and securedpermanently in place by welding through the fourholes and building the welds up above the surfacefar enough that they can be dressed back flush.TIG welding is ideal for this. If this is doneproperly, no trace of the welds will show.
A cube of steel 1/2” x 1/2” x 1/2” is likewisewelded in place on what will be the exact bottomcenter of the receiver blank. It should be relievedon all four sides where it joins the receiver andbuilt back up above the surface with weldmaterial and machined back flush. The forwardedge should be flush with the receiver face.
The assembly is now chucked in the lathe andthe barrel bushing bored to .875 inch. Thereshould be .500 inch of the bushing extending pastthe front face of the receiver. This is turned to adiameter of 1.125 inches and threaded 24threads per inch.
For both receivers to mate properly and theinside diameters of both the upper receiver andthe lower receiver spring tube to be concentricand parallel, .100 inch of material must beremoved from the exact bottom side of the upperreceiver. The centerline of the front hinge block isused as a reference point and the flat machined asindicated. This is best done with the millingmachine, using a face mill or other large-diameterend mill. The radius at the bottom rear should becut to match the contour of the lower receiver asclosely as possible. This can be accomplished inseveral ways. Probably the easiest way is throughuse of a rotary table in the milling machine.Another way is through use of a radius-cutting—or corner-rounding, as some call them—end mill.In lieu of either of these, it can be formed by handusing a disc sander. If care is used and the fit ischecked frequently, this method will achieve thesame result as the others. It will just take longer.
Whichever method is used, when the fit is asclose as possible, both receivers should be clampedtogether and the front hinge pin hole drilled.
Before the hole is drilled, however, a bushingis turned to fit the lower receiver front hinge pinhole closely, and a 1/8-inch hole is drilled throughthe center. This bushing is placed in the fronthinge pin hole of the lower receiver, and the holeis drilled through the upper receiver hinge blockusing a 1/8-inch drill. The receivers are thenseparated and the hole enlarged to full size usinga 1/4-inch drill. The purpose of the drill bushingis to protect the soft aluminum lower receiverfrom damage caused by use of a full-size drill or
Welding completed.
Barrel bushing and front hinge block are welded in place.
13
UPPER RECEIVER
mutilation from metal chips or shavings.If the shop-made steel receiver pictured in the
Preface is used, the drill bushing is not necessarysince the hole is drilled through both receiverssimultaneously.
If a new commercial receiver or the shop-made receiver is used, or if you have means toremove the recoil spring tube from your existingreceiver, a better fit can sometimes be obtainedby turning a close-fitting mandrel to fit inside theupper receiver and using a cap and drawbolt topull it back tightly against the lower receiver atthe rear end before clamping and drilling. Withthe cross pin in place, the upper receiverassembly should swivel from the closed position
to almost a right angle. The bottom, front, andrear of the mounting block must be shaped to ahalf round configuration to permit this.
A bracket to accept the rear mounting crosspin is made by welding a 1/2-inch steel cube tothe outside surface of a section of 1 1/4-inch-outside-diameter tubing. This should have a wallthickness of .065 inch and a length of .625 inchto .650 inch. The side of the cube adjacent tothe tubing should be radiused to fit the tubingclosely with the sides and ends angled. Theseam, or joint, is built back above the surface bywelding. The weld joints are then dressed backflush with the surface and the block widthreduced to .475 inch.
Drill bushings. Drilling front hinge-pin hole.
Shop-built upper, clamped to commercial lower withbushing in front pin hole, ready for drilling.
Pistol upper unit, ready for mounting.
14
.25
0” D
IA.
DR
ILL AFTE
R A
SS
EM
BLY
RE
AR
MO
UN
TIN
G B
RA
CK
ET
BE
VEL FO
R W
ELD
ING
1.2
50
”
.50
0”
.50
0”
.70
0”
.06
5”
Diagram #3
15
UPPER RECEIVER
A slot to accept this block is cut at the bottomrear of the upper receiver to the dimensionsshown in Diagram #2. The slot to clear thehammer can also be cut at this time, as well asthe magazine opening, including a slot to provideclearance for the ejector.
If a commercial lower receiver is used, eithera relief cut must be made in the left side of theupper receiver to clear the bolt-hold-open releasebutton or the bolt-hold-open device must beremoved. This cut can be located by measuringback from the front face of the receiver as shownin Diagram #1. A simpler method, however, is toposition both receivers in their respectiveassembled positions and mark around the hold-open button. The relief cut is not necessary if theshop-made receiver is used. Since the 9mmmagazine does not extend to the rear far enoughto activate the bolt-hold-open, there is no point inputting it in the receiver.
With the completed bracket and the front hingepin in place, both receivers are clamped together,and, using the bushing as before, the mounting pinhole is drilled. Again, the drill bushing is requiredonly if the commercial aluminum receiver is used.As with the front hole, both receivers are drilledtogether when using the shop-made receiver. Withboth pins then in place, a close-fitting assemblywithout any shake or play should result.
Cut near center to clear bolt release.
Completed receiver assembly.
Upper receiver with rear mounting bracket in place.
16
THE AR-15/M16
An ejection port is machined in the right side,as shown in Diagram #2. There are people whowill insist that this port need not be nearly as bigas the one shown. They will tell you that it iseasier for dirt and debris to get into the large port.They do not tell you that it is also easier for dirtand debris to get out of the large port. There isalso less chance of empty cases striking the edgesof the larger port and falling back in the action,causing the gun to jam. This has happened onnumerous occasions with small ejection ports.Make your choice.
The lengthwise slot, to accommodate the
cocking lever, or charging handle, is cut in theleft side in a 10:30 o’clock, or 315˚, position (45˚above the centerline) when viewed from the rear.The “dog leg” at the upper rear serves as a safetyin the open-bolt version. Although it is notrequired for the closed bolt, it will serve as a bolt-hold-open if included.
A 1/8-inch-wide slot, .200 inch long, must becut beginning at the front face of the threadedbarrel bushing and on the top centerline. Thelocating pin on the breech end of the barrel fitsinto this and keeps the barrel located in itscorrect position.
Slot is cut for barrel-positioning pin.
17
While three different bolt assemblies areshown in the following diagrams, they have acommon configuration as far as the size andshape of the magazine cuts, the bolt nose, andthe extractor cuts. One version is for use in theopen-bolt gun and has a fixed integral firing pin.Another, which is the same length and diameter,is intended to be contained entirely inside thereceiver, making possible a closed-bolt pistolversion. The third is a full-length bolt intendedfor use with the original recoil spring and buffer.This is the one to use if the unit is to beinterchanged with the original .223 upperreceiver assembly.
Even though several of the dimensions are thesame for all three, we will discuss the constructiondetails of each one separately. This will entailsome repetition but may also avoid confusion.
OPEN BOLT
The open-bolt version should be cut to lengthwith both ends squared. A bolt nose is turned onone end of the bolt body. This should extend .150inch forward from the bolt body proper and havean outside diameter of .550 inch if used as a9mm. The .45 version should be .650 inch. Acounterbore slightly larger than the cartridgehead is cut .100 inch deep. This should have aninside diameter of .400 inch for the 9mm or .480inch for the .45. In the center of this, a fixed
firing pin, .060 inch in diameter, is formed. Thisshould have a hemispherical point and protrude.050 inch from the bolt face. A fairly simple wayto form this is to chuck an open-center, or non-center-cutting 3/8-inch end mill, in the lathe tailstock drill chuck. With the bolt turning in theheadstock chuck, the end mill is fed into the boltface with the tail stock. This will form the insidediameter some .020 inch to .025 inch undersize
(BOLT
From left: full-length bolt, open-bolt assembly, closed-boltassembly.
18
OP
EN
BO
LT
.37
5” D
IA.
2.5
00
”
.38
6” D
IA.
TOP
VIEW
BO
TTOM
VIEW
.80
0”
.12
5”
2.0
0”
2.5
00
”.1
50
”
4.2
00
”
1.0
50
”
.80
0”
2.1
00
”
RIG
HT S
IDE
.35
0”
.45
0”
.25
0”
1.1
25
”
.06
0” D
IA.
.40
0” D
IA. (9
MM
).4
80
” DIA
. (.45
)
.55
0” (9
MM
).6
50
” (.45
)
Diagram #4
19
BOLT
in the case of the 9mm, and the open center ofthe milling cutter will leave a small projectionthat can be turned to form the firing pin using alathe cutting tool ground to form it. The outsidecutting edge of this same tool is used to bring thecounterbore to the correct diameter.
With this accomplished, the bolt is reversedin the lathe chuck, whereupon a hole of sufficientsize to accept the recoil spring is drilled, as shownin Diagram #4. The hole diameter should beslightly larger than the spring used to assure freemovement of the spring as it compresses.
In the prototype gun, the spring usedmeasured .375 inch in diameter. The hole wasdrilled with a “W” drill measuring .386 inch indiameter. A 25/64 drill, which measures .3906inch, would be equally satisfactory. A slight bevelshould be formed at the entrance of the hole,which will assist in reducing friction and binding.
While the bolt is chucked in this position, therear end of the body can be reduced in diameteras shown in the diagram. This is required to allowthe bolt to travel entirely to the rear of thereceiver, with the smaller-diameter portionmoving freely inside the rear mounting bracket.
The bolt is now secured in the millingmachine vise and a slot cut down the exact center
using a 5/8-inch end mill. The slot should be cutto a depth that just meets the outside diameter ofthe bolt nose and a length of 2.250 inches. Uponcompletion of this, a deeper slot is cut along eachside of the cavity using a 1/8-inch end mill. Theseare to provide clearance for the magazine lips andthe ejector. The slot on the extractor side shouldbe cut to a depth slightly less than that of theinside counterbore. The other side must be cutapproximately .100 inch deeper to clear theextractor. Properly done, this will leave a strip 1/4inch wide that is the same depth as the bottom ofthe bolt nose. These slots must be cut longenough to clear the back side of the magazine onthe one side and the rear of the extractor on theother. Next the bolt is rotated 15 degrees and acut made down the side. It is then rotated back30 degrees in the other direction and a matchingcut made. These will closely match the magazinesides while providing ample clearance betweenthe bolt and magazine.
The extractor cut is made with a 1/8-inch endmill in a ten o’clock position when viewed fromthe front. The slot should be cut to the insideedge of the bolt nose counterbore. A springpocket is cut to the same depth at the extremerear end of the slot using a 3/16-inch end mill.
Magazine clearance is cut with end mill.End view showing bolt nose configuration.
20
Diagram #5
CL
OS
ED
BO
LT
.26
6” D
IA.
1.2
50
”.8
00
”2
.70
0”
TOP
.10
0”
.40
0”
.55
0”
.15
0”
BO
TTOM
1.2
00
”
1.0
05
0”
.49
0” D
IA.
.26
0”
.37
5” D
IA.
.25
0” D
IA.
.15
6” D
IA.
.62
5”
.06
5”
2.0
0”
.57
5”
.87
5”
.80
0”
RIG
HT S
IDE
4.2
00
”
21
BOLT
CLOSED BOLT
The short closed bolt is made in the samemanner and to the same outside dimensions,except that instead of the fixed firing pin, a .070-inch hole is drilled in the center of the boltcounterbore. A No. 50 drill is correct for this.Before the counterbore is cut, this hole should bestarted with a center drill, fed by the tail stockchuck. The drill is then used to drill the smallhole approximately 1/2 inch deep. The exactdepth doesn’t matter since a larger hole, drilledfrom the opposite end, will enlarge most of it.This small drill should be withdrawn and cleanedfrequently, and amply lubricated. Otherwise itmay very well seize and break off in the hole. Ifthis should happen, you might as well get anotherpiece of material and start over, since that wouldprove far easier than getting the broken drill out.
The counterbore can now be cut to its fulldepth and diameter, removing any trace of theoversized hole made by the center drill.
Since the firing-pin design used in theoriginal bolt would be hard to improve on, we willuse it in our bolt. A surplus military firing pinshould be acquired before the bolt is machined toaccept it. These are plentiful at present, and at agood price. If none are available, one can be latheturned using the dimensions and directionsshown in the Small Parts chapter (Diagram #42).The bolt body is reversed in the lathe chuck and,starting the hole with a center drill, an opening to
accept the firing pin is made. This opening willconsist of three diameters, four if the firing pinhole nose hole already drilled is counted. Start bydrilling with a 1/4-inch drill to a depth of 3inches. This depth need not be exact, but closeapproximation should be kept. This is followed bydrilling with a 3/8-inch drill to a depth slightlyless than 1.450 inches.
This portion requires a square, or flat,shoulder at the bottom. It can be formed by usinga 3/8-inch end mill to reach the final depth. Thisshould be as close to the previously mentioneddepth of 1.450 inches as possible. A smaller hole,.120 inch in diameter, extends from the bottom ofthe 1/4-inch-diameter portion to a point justbehind the bolt face. This should have a totaldepth of 4 inches. Since ordinary twist drills ofsufficient length are not normally available fromhardware stores and the like, and even thoseobtained through special order are limber andsubject to easy breakage, we can make up asuitable drill for this purpose fairly easily.
Chuck a piece of 1/4-inch drill rod that is atleast 4 inches long (7 inches if you ever intend tomake up the full-length bolt described next) and,using the tail stock chuck, drill a hole in one endusing a No. 31 drill. This, of course, is startedwith a center drill, which by now should bestandard practice. The drill is then reversed and,with a small amount of flux applied, pushed intothe hole just drilled and silver-soldered in place.The end of the drill protruding from the drill rod(it should protrude at least 1 inch) must beprotected from the heat used to silver-solder it inplace to prevent drawing the temper. It will likelybe necessary to polish the larger 1/4-inch sectionwhere it was heated before it will enter the holefreely. The depth of these holes can be regulatedclosely through the use of stops made byfastening close-fitting collars around the drillstems, or extensions, with the exact length to drillthe holes extending. Such collars can be fastenedin place with solder or epoxy.
This bolt design requires two small-diameterrecoil springs located on either side of the firingpin. The recoil springs used in the military M1carbine are well suited for this. They are plentifuland cheap. The diameter of these isapproximately .260 inch. The holes to accept
Open bolt (left) shows fixed firing pin. Closed bolt (right)shows firing pin hole.
22
THE AR-15/M16
these should be slightly larger for clearance. A17/64-inch drill, which measures .2656 inch, willserve well for this. These holes should be 2.700inches deep and measure .800 inch apart fromcenter to center with .400 inch on each side ofthe centerline.
A slot must be cut, as shown in the drawing,to permit the hammer to move forward farenough to contact the firing pin. This is done byclamping the bolt in a vertical position in themilling machine and cutting it with a 3/8-inchend mill. This slot should be .875 inch deep,provided that the overall length of 4.200 inchesis adhered to. This will provide a shoulder so thatwhen the hammer is fully forward the firing pinwill protrude .050 inch through the bolt face.The distance from the extreme front of the boltnose to this shoulder should be 3.325 inches.Firing pin protrusion can be checked and verifiedby pushing the firing pin forward—preferablywith the return spring in place—flush with theshoulder and measuring the protrusion with adepth micrometer.
At the location shown in Diagram #5, acrosswise hole is drilled for a pin to keep thefiring pin in place. A close-fitting plug should beinserted in the firing pin hole while this hole isdrilled to provide support for the drill. Otherwisethe drill will “creep” or “crawl” toward theunsupported side and almost certainly break.
Bolt assemblies showing springs and spring guides.
Lower side view of both bolts.
23
BOLT
FULL LENGTH
The full-length bolt, which is to be used withthe original recoil spring, is made in the samemanner except that in this case it will have anoverall length of 6.950 inches. The rear portion,measuring 3.750 inches long, is turned to adiameter of .990 inch. This assures that it willslide, without binding, inside the spring housing.
This time, the hammer slot must be cut as shownin Diagram #6, with a flat shoulder 3.325 inches tothe rear of the bolt’s forward face, as before, and ofsufficient length to allow the hammer to travelforward and back without interference. While notactually necessary, it is easier to cut this slot all theway through the bolt body from top to bottom thanthe partial depth required.
The extractor pin holes are in the samelocation on all three versions and should bedrilled with the extractor clamped in place toensure that they line up exactly.
The cocking lever, or operating handle, isalso of the same dimensions and in the samelocation on all three versions. The correctlocation for the hole in the bolt is fixed bymarking its location through the receiver slotwith the bolt in place and in the closed position.The operating handle must not contact the frontof the slot. If possible, this hole should be drilledin the milling machine with a slightly undersizeddrill and finished with a 3/8-inch end mill,forming a flat bottom in the hole.
Open bolt on left; closed bolt on right. Rear view of open bolt (left) and closed bolt (right).
24
FU
LL
-LE
NG
TH
BO
LT
.95
0”
.37
5”6.8
70
”
TOP
VIEW
.37
5”
1.5
00
”
3.7
50
”2
.97
0”
3.2
00
”
1.2
50
”
.15
0”
SID
E VIE
W
1.5
00
”
Diagram #6
25
The barrel(s) used in this project require aretaining ring measuring 1 inch in diameter.Therefore a barrel blank with a minimum diameterof 1 inch must be used. At present, a number ofbarrel manufacturers offer suitable barrel blanksfor this. Most, in fact, offer such blanks with a 1-inch diameter and a length of 24 inches. Sincethese usually come slightly longer than theadvertised length, it is possible to cut four full 6-inch-length pistol barrels from one of these—evenafter allowing for saw cuts and squaring the ends.We can also get both a 6-inch pistol barrel and an18-inch rifle barrel from one such blank.
The pistol barrel can be of whatever length youchoose. Although Diagram #7 shows my personalpreference of a 6-inch barrel, there is no goodreason why yours should not be longer or shorter ifyou so desire. I have always thought a 6-inch barrelhas a more balanced look than other lengths.
(BARREL
Rifle and pistol barrels made up several years ago forsquare receiver model but interchangeable.
Rifle barrel shown with unturned blank.
26
THE AR-15/M16
The rifle barrel, though, is required by federallaw to have a minimum length of 16 inches. Ourbarrel should be made slightly longer than theminimum length, simply to assure that even thestupidest law enforcement agent will beconvinced that it is of legal length.
It has long been accepted by the moreintelligent authorities that if a rod is insertedin the muzzle end of a barrel and pushed inuntil it contacts the bolt face, this length willbe accepted as the barrel length. There are,however, any number of idiots that have neverlearned this. In fact, I can remember aninstance where a stupid small-town marshalthought he was going to confiscate a shotgunof my manufacture, which I was displaying at agun show, because the barrel only measuredsomething over 17 inches from the muzzle tothe point where it entered the receiver. Nevermind the fact, which I tried to explain to him,that there was another inch of barrel extendingback into the receiver. It was too short andsubject to confiscation, or so he said. Luckily,a state trooper (these are usually considerablysmarter than other law enforcement officers, atleast in this part of the country) happened byand straightened him out. But I could havehad to go to considerable trouble to get my gunback. This example should serve to illustratethe convenience of a slightly longer barrel. Theone shown in the diagram is 16 1/2 inchesoverall, mainly because this was the length of
my barrel blank. Eighteen inches would havebeen more desirable.
Threaded muzzle ends, to accept muzzlebrakes, flash hiders, and the like, may also bedetermined to be illegal. (Some of the samepeople mentioned above will think you intend tomount a silencer if the muzzle is threaded.) Ifsuch devices are used, they should be fastened inplace permanently—preferably by pinning orsilver-soldering. Bayonet lugs are also ofquestionable legality and should be avoided.
You will also need a way to cut the chamber.At present a number of companies manufactureand sell chamber reamers in almost any caliberone could wish for. These usually range in pricefrom $40 to $100. Since the straight-cased pistolcalibers required in this project use chambersthat are only slightly larger than the bore, andonly a small amount of metal is removed whencutting the chamber, only a finish reamer will benecessary. When larger bottlenecked cases areused, it is a good idea to remove the bulk of thechamber metal with a roughing reamer, whichwill cut the chamber slightly undersize, andfollow it with the finish reamer. This is doneprimarily to prolong the useful life of the finishreamer. Be sure to specify that the reamer will beused in a rifle barrel when ordering it. A goodmany reamers for pistol calibers are made withthe pilot ground to groove diameter or slightlylarger for use in revolver cylinders. These will notenter the bore of the rifled barrel, which requires
Barrel is turned to desired diameter. End turned to length, squared.
27
.80
0”
.610
”
9.0
0”
.62
6”
.87
5”
.60
0”
TO .6
25
”
.60
0”
PIS
TOL
BA
RR
EL
.60
0”
7.0
0”
MIN
.
RIF
LE B
AR
RE
L
.06
5”
.87
5”
45
˚
1.1
00
”
.12
5”
BA
RR
EL
IND
EXI
NG
PIN
BA
RR
EL
S
Diagram #7
.90
0”
.12
5”
28
THE AR-15/M16
a reamer pilot of bore diameter or slightly less. Ofcourse, most 9mm and .45 ACP cartridges areused in full and semiautomatic arms, but thereare also revolvers chambered for these calibers.Just to be on the safe side, go ahead and specifythat the reamers are for rifle barrels.
It should be noted that the higher-pricedreamers will usually come with an integral throatreamer, allowing you to perform the entirechambering operation with a single reamer.Many times the cheaper ones will require the useof a separate “throating” reamer to cut thisportion, which is actually a bullet seat. Thehigher-priced reamers such as those made byClymer Manufacturing Co. will usually prove tobe the cheapest in the long run, or at least themost convenient.
Construction of the barrel is a fairly simpleprocess. The barrel blank is cut to the desiredlength and the ends are squared in the lathe.Don’t be surprised if, once the barrel blank hasbeen cut in two, the bore is not concentric withthe outside diameter. This is a fairly commonoccurrence, especially with cheaper barrel blanks.If such is the case, the barrel should be mountedbetween centers and the entire length turnedround. The breech end is then turned to adiameter of .875 inch for a length of 1.125inches. Just ahead of this cylindrical section,which fits inside the upper receiver, a flange .125inch wide and 1 inch in diameter is formed. Theremainder should be turned to a diameter of .600to .625 inch if used in the 9mm pistol version.The .45-caliber pistol version should be .650 inchor slightly larger in diameter.
The rifle barrel is made in the same fashion,with the same dimensions at the breech end. Theportion directly forward of the retaining flange canbe slightly larger than the pistol version for a lengthof 6 inches if desired. The remainder, or the portionthat extends past the fore-end, can be turned assmall as .550 inch in diameter for the 9mm andshould be no larger than .615 inch. This should bethe minimum diameter for the .45 barrel. Justforward of the fore-end’s front face, two bandsshould be turned to a diameter of .626 inch. Theseshould be 1/2 inch in length with a relieved section(.610 to .615 inch diameter) .900 inch in length
between them. This will allow a military surplusM16 front sight to fit snugly over the two bandswhile sliding freely over the barrel until almost inplace. This is done primarily to avoid marring thefinish when assembling the finished gun.
A 45-degree “approach cone” is formed in thebreech end of the barrel to aid in feeding. Withthis type of feeding system, which is similar tothat used in the 1903 Springfield, 1917 Enfield,M54 and M70 Winchesters, as well as severalothers, the bullet is positively guided into thechamber as it moves forward. This tends toeliminate the “stovepiping” and hangups on theend of the barrel that are fairly common withsome other systems.
The muzzle should be crowned with arounded outer edge and a convex curve on theinside. This will leave a sharp edge where thebore exits the barrel instead of the rounded curveoften seen. A lathe cutting tool is ground to formthis contour. It can be brought to a high polishwith progressively finer grits of abrasive cloth andpaper. This type of crown is fully as accurate asthe so-called “target” type flat crown with asecond flat counterbore inside, which, although ithas been used for at least a hundred years, is“discovered” at frequent intervals by some of thenewer gunsmiths.
Proper depth of the chamber is determined bymeasuring from the front face of the receiver tothe bolt face, making sure the bolt is fully forwardwhile this measurement is taken. Anothermeasurement is taken from the breech end of thebarrel to the retaining flange. This measurementwill be slightly longer than the first, so thesmaller (first) number is subtracted from thelarger. The result will be the depth of thecartridge head below the end of the barrel.
The chamber is cut by feeding the reamerinto the end of the barrel that is chucked in thelathe and turning at the slowest speed available.Pressure from the tail stock ram is used to pushthe reamer into the bore. Do not attempt to holdthe reamer with the tail stock chuck. It must bekept from turning by using a hand-held tapwrench, a clamp, a small wrench, or some similararrangement that can be released and allowed toturn with the barrel in the event the reamer
29
BARREL
Approach cone is cut in breech end.
Breech end of barrel, showing approach cone.
Indexing pin is pressed in place using vise jaws.
30
THE AR-15/M16
should seize. The reamer should be kept welllubricated and withdrawn and cleaned frequently.
Supporting the drive end of the reamer on atail stock center should only be done when thebore is absolutely concentric, without runout, andthe tail stock is absolutely in line and centeredwith the bore. Otherwise, a flat-faced center witha small dimple in the middle should be used topush the reamer.
Another method is to clamp the barrelbetween wood blocks in a vise and turn thereamer by hand using a suitable tap wrench or
reamer drive. If this method is used, care must betaken to hold the reamer straight and in line withthe bore, with no sideways pressure exerted inany direction.
A small hole is drilled, as shown in Diagram#7, using a No. 31 drill, and after a slight taper isground on one end, a locating pin made from1/8-inch drill rod is pressed into it. This causesthe barrel to be replaced in the same positionafter removal.
The extractor slot is located and cut asdescribed in the chapter on fitting and assembly.
31
If the commercial lower receiver assembly isused, we will only need to concern ourselves withthe barrel shroud, as used on the pistol version,or the fore-end, as used on the rifle. Both areidentical except for overall length and the factthat a cap is welded in place in the front end ofthe rifle fore-end.
Each is begun by turning a barrel retainingnut to the shape and dimensions shown inDiagram #9. It is threaded on the inside to screwon the front end of the receiver. It has a shoulderinside that bears against the barrel flange whentightened, securing the barrel in place. This nutshould be made from a better grade of steel suchas 4140 or automobile axle material. The threadsmay stretch and wear rapidly if low carbon steelsuch as 1018 is used.
The cylindrical portion can be made fromalmost any thin-walled tubing of the correctoutside diameter. Since there is no strengthrequirement here, even muffler pipe can be used,provided the unsightly seam that is usuallypresent is acceptable. Discarded automobileshock absorbers are a good source for materialsuch as this, provided the right size can be found.Actually, the outside diameter can be adjusted upor down to accommodate the available material.In fact, when used with the pistol version, abarrel shroud slightly smaller than the receiverdiameter would probably look better than the oneillustrated in Diagram #8.
Both versions should be a snug fit over theoutside of the nut and are welded or silver-soldered in place. The rifle version should havean end cap, which is turned to a snug fit insidethe tubing and then welded or silver-soldered inplace at the forward end. It must also have a holebored through the center, slightly larger than thebarrel diameter.
The ventilating holes in the shroud body can bespaced to suit your taste. The prototype had fourrows of 1/2-inch holes spaced 1.200 inches apart.These can be accurately and easily spaced anddrilled in the milling machine. If the holes arestarted with a center drill and finished with aradius-nosed 1/2-inch end mill, smoother holes willresult than if the work is done with a twist drill.
Commercial pistol grips are available from anumber of sources, some with the originalmilitary configuration and others with numerousmodifications and refinements. These areavailable at such low prices that it would seemfoolish to manufacture one.
Should it become necessary, however, it is afairly simple matter to build one. A block ofwhatever type of hardwood that suits your fancyis obtained. Since it only needs to be 1 1/4 inchesthick, 2 1/4 inches wide, and 5 inches long, sucha scrap can usually be found at a cabinet orcustom furniture shop. Custom gun stock makersand knife makers are also sources for these.
The outline is drawn on the side of the blank
(BARREL SHROUD,STOCK, AND GRIP
32
FO
RE
-EN
D
Diagram #8
5.2
50
”
2.0
”1
.25
0”
1.2
50
”1
.25
0”
1.5
00
”
6.5
00
”
RIFLE
VER
SIO
N
PIS
TOL VE
RS
ION
33
FO
RE
-EN
D C
OM
PO
NE
NT
S
Diagram #9
BO
RE
1.0
80
” TH
RE
AD
1.1
25
” x
24
TU
RN
TO
A S
NU
GFI
T IN
SID
E T
UB
ING
.85
0”
.30
0”
1.5
00
”.6
50
”
.20
0”
1.3
75
”.7
00
”
.30
0”
BA
RR
EL
NU
TFR
ON
T P
LUG
1.5
00
”
34
THE AR-15/M16
using the pattern shown in Diagram #10, orwhatever profile suits you, and cut to shape. It isthen clamped in the milling machine and the topside is shaped to mate with the receiver. The topand front side where it fits against the receiverare milled flat and square. This is followed bycanting the blank at the required angle andcutting the slot. The hole for the mounting boltshould be drilled while this angle is set. Thehole’s location can be determined by measuringfrom the center of the bolt hole in the receiver tothe flat part of the receiver that the grip adjoinsand transferring this measurement to the gripblank. The grip is then reversed and either acounterbore to clear the head of the mountingbolt hole or a cavity similar to the one found inthe commercial grip is cut in the lower end. Thisshould be parallel to the mounting bolt hole, andit can be done with a 5/8-inch end mill.
The outside contour is formed using thesanding wheel to rough-shape it and finishingwith rasp files and sandpaper in progressivelyfiner grits (starting with 50 or 60 grit andfinishing up with 400 grit).
The finish used can be any kind or color thatstrikes your fancy, from clear gun stock finish tocamouflage paint. The grip shown in thephotographs was made from a walnut block and
given several coats of automobile primer. Thiswas followed by several coats of flat black enamelin an attempt to match the color of the buttstock. My only reason for building it in the firstplace was that I wanted it on a certain day andnone were available locally. A bit of planning andordering ahead would have saved me this extrawork, but I suppose I need the experience.
The butt stock, as available on the surplusparts market, is another bargain. Mounting it inplace presents no problem. If the action springand buffer housing are on hand, you simply screwit into the lower receiver and slip the butt stockover it. It is held in place by a screw that installsthrough the butt plate.
When the short, self-contained bolt assemblyis used, this part is not necessary. A plug is turnedfrom aluminum (if available—to save weight) tothe dimensions shown in Diagram #11 andthreaded to screw into the lower receiver. It isdrilled and tapped in the center for a 1/4 x 28thread. A draw bolt, which extends to the rear ofthe stock, is cut from 1/4-inch drill rod andthreaded with the same 1/4 x 28 thread to screwinto the receiver plug. A 3/8-inch-diameter sleeve,1 1/2 inches long, is drilled to approximately halfdepth with a 1/4-inch drill, slipped over thesmooth end of the draw bolt, and silver-soldered
Grip was made of walnut, painted black simply because I didn’t have a plastic military-surplus grip on hand.
35
SH
OP
-MA
DE
GR
IP
Diagram #10
.38
0”
.90
0”
1.3
00
”.2
00
”
1.8
00
”
1.9
50
”
1.1
50
”
4.3
50
”
30
˚
36
Diagram #11
ST
OC
K B
OL
T P
AR
TS
RE
QU
IRE
D T
O M
OU
NT
SU
RP
LU
S M
16/A
R-1
5 B
UT
T S
TO
CK
THR
EA
D .2
50
” x 28
.15
0”
.40
0”
BR
EE
CH
PLU
GS
TOC
K P
LUG
THR
EA
D .2
50
” x 28
x 1.0
0”
1.1
40
”1
.14
0”
1.1
40
”
1.1
87
”.2
50
”.7
50
”
.60
0”
1.3
00
”
.55
0”
.25
0”
.65
0”
.25
0”
9.0
0”
1.1
50
”
37
Diagram #12
RE
AR
RE
CE
IVE
R C
AP
FO
R O
PE
N-B
OL
T P
IST
OL
VE
RS
ION
BO
RE
.2
17
” TH
RE
AD
.2
50
” x
28
DE
LETE
SP
RIN
G G
UID
E W
HE
NU
SE
D W
ITH
CLO
SE
D B
OLT
.85
0”
1.2
00
”
.25
0” .40
0”
.85
0”
3.8
50
”
THR
EA
D .2
50
” x
28
THR
EA
D 1
.18
7”
x 1
6
.25
0”
.60
0”
.20
0”1.3
00
”1
.37
5”
38
THE AR-15/M16
in place. The remainder is drilled and tapped fora 10 x 32 screw. This arrangement allows the buttstock to be positioned in place and a short 10 x32 screw installed through the butt plate, which,when tightened, holds the butt stock in place.
For a full-grown man, it is desirable that thebutt stock be somewhat longer than the lengthprovided by the standard military M16 butt stock.
For some reason, our military has always—evenfrom flintlock musket times—used rifles with ashort enough length of pull to accommodate thevery smallest shooter, and everyone else isexpected to adapt to it. The butt plate portion canbe removed by sawing and squared with thesanding wheel, after which a recoil pad is epoxiedin place. This will lengthen the pull by 1/2 to 1
Breech plug screws into lower receiver. Through-bolt screws into rear end of plug.
Surplus M16 butt stock is mounted using through bolt and breech plug adaptor. Recoilpad is added for extra length.
39
BARREL SHROUD, STOCK, AND GRIP
inch, depending on the thickness of the pad. Ifthis is done, another close-fitting aluminumspacer is epoxied in place in the rear end of thestock. It should also be pinned in place with a 1/8-inch steel cross pin, installed through a holedrilled through the plug and both stock walls. Thisshould be drilled offset from the center hole so asto not interfere with the draw bolt. The outside
end of this plug should be counterbored to accepta bolt head, which is welded or silver-soldered tothe end of the stock bolt, replacing the threadedsleeve. This should be a bolt head that accepts anallen wrench. If the upper mounting screw hole inthe recoil pad is enlarged enough to clear the allenwrench, the butt stock can be installed or removedwithout the bolt head showing.
Breech plug partially screwed in place.
Through-bolt is secured using allen wrench through recoil pad.
40
THE AR-15/M16
If the time ever comes when the military-typestocks are no longer available, it will be simpleenough to make a butt stock from hardwood, justas we did the grip. This would require a draw bolthole extending from the front face of the stock,partway through to the rear, with the remainderenlarged to clear the bolt head. The threadedplug in the receiver would be counterbored at therear to accept a round tenon, machined or carvedon the front face of the stock. A short metal pin,which fits into the recess in the receiver to keepthe stock from turning, would be threaded intothe stock face just below the tenon. Your choiceof butt plate or recoil pad is fitted to the butt endand the assembly shaped and finished in the samefashion as the grip.
Finished fore-end installed on completed gun.
Grip, butt stock, and adaptor.
41
Sights, as used on the pistol version, arepractically identical to those used on my otherpistol designs, differing only in that the radius atthe base is slightly larger. At the risk of beingconsidered repetitious, I will include directionson how to make such sights here for those whodon’t have my other books.
Experience has shown me that elaborateadjustable sights are not necessary on the pistolversion of this gun. A simple blade front sight anda fixed, square-notched rear, when aligned andcut to the proper heights, are completelyadequate for a gun of this type.
Bases, complete with protective ears, can
easily be formed from 16-gauge sheet metal usinga vise, form blocks, and a heavy hammer.
The form block, which can be used to formboth front and rear bases, is made by cutting aradius to match the contour of the receiver on thelower side of a steel block. Since the receiver is 11/2 inches in diameter, the radius cut shouldmatch this plus the thickness of the sheet metalused. The block should be .625 inch wide by .750inch high and at least 1 inch long. This will formthe inside of the sight bases. A short length of 11/2-inch-diameter round stock is used to form theconvex bottom side, which fits against thereceiver. Two 1/8-inch-diameter holes, .625 inch
(SIGHTS
Pistol sight blanks shown with form die. Blank is placed on form die.
42
Diagram #13
PIS
TO
L S
IGH
TS
FOR
M FR
OM
14
ga. SH
EE
T ME
TAL B
LAD
ES
FRO
M .1
25
”
FRO
NT S
IGH
T
.62
5”
.70
0”
.62
5”
.70
0”
1.4
00
”
1.0
50
”
.40
0”
.70
0”
.12
5” X .7
50
” SLO
T
.45
0”
.12
5” X .6
25
”
SLO
T
43
SIGHTS
apart, should be drilled on center, completelythrough the form block. These should continuepartway through the lower, round form block.Locating pins installed in these holes keep theassembly aligned while in use.
Blanks are cut, as shown in Diagram #13,with holes drilled to match the locating pin holes.The bases will form more easily if left in arectangular shape until formed and the uprightears cut to shape after forming. With the locatingpins in place, the blank is positioned betweenboth form blocks and the assembly clamped, withone side down, in the vise. When the vise istightened, pressure from the vise jaws will formthe radiused bottom portion.
Sides are folded over with hammer.Formed to shape in vise.
Formed front sight base with blade.
Rear sight base with sight blank.
Formed rear sight base.
44
THE AR-15/M16
The part of the blank extending above theform blocks is bent, or folded, flat against the sideof the form block using a block and heavyhammer. At this point the assembly is reversed, orturned over, in the vise and the process repeated.It is helpful to place a spacer, or a series of blocks(sometimes called “blocking up”) between thethroat of the vise and the bottom of the partbeing formed. This will prevent both the workand the form blocks from being driven deeper inthe vise when forming.
A slot is cut crosswise in one base to receivethe rear sight cross piece and lengthwise downthe center of the other for the front sight blade.These can be cut with a 1/8-inch end mill, or, ifnecessary, with a high-speed hand grinder using acut-off blade.
The blades are fluxed and silver-soldered inplace in the bases. Both assemblies are thenclamped in place on the receiver and silver-soldered. Both sights can be kept in alignmentduring mounting by placing a close-fitting (5/8-
inch-wide) piece of square stock, long enough toreach across both sights, inside both bases andclamping it in place before mounting.
For those who absolutely must haveadjustable sights, the rear sight cross piece can beomitted and the base drilled and tapped for aWilliams “Guide” rear sight, which is adjustablefor both windage and elevation. A Marble #20rear sight, which is almost identical to thealuminum Williams sight except that it is made ofsteel, can also be used. Either of these will servethe purpose. If you simply must have one that youmade yourself, my book entitled Home WorkshopWeapons for Defense and Resistance: Vol. I, TheSubmachine Gun contains a description of onethat is adaptable.
The rifle version requires the combination ofa rear sight base and a carrying handle thatelevates the rear sight to the same height as thecommercial gun.
The base is made by cutting a blank to theshape and dimensions shown in the drawing from
Sights mounted in place.
45
Placed in vise against form block.
Rifle rear sight base is cut from 12 ga. sheet steel.
Diagram #14
RIF
LE
RE
AR
SIG
HT
PA
TT
ER
N
.70
0”
.62
5”
2.3
00
”
4.6
00
”9
.20
0”
2.3
00
”
46
THE AR-15/M16
12-gauge sheet metal. The blank is then clampedin the vise against a form block of 5/8-inch-thicksteel bar stock, which should be at least 3/4 inchwide and 5 or more inches long. Here again, thisform block should be supported by blocking it upbetween the bottom of the block and the throat ofthe vise. When struck with a heavy hammer, worksuch as this has a tendency to move downwardbetween the vise jaws unless supported
underneath. The portion extending above the foldline is bent flat against the side of the form blockusing the hammer and a flat piece of bar stock.When formed, the assembly is turned over andthe opposite side is formed in the same manner,creating a hollow trough. The sides are thenshaped to the profile shown in Diagram #14 orwhatever shape appeals to you.
Shaped rear sight.Sides are formed with black and hammer.
47
RE
AR
SIG
HT
/CA
RR
YIN
G H
AN
DL
E R
IFL
E V
ER
SIO
N
Diagram #15
.62
5”
.90
0”
.55
0”
.80
0”
2.1
00
”4
.50
0”
7.3
75
”
.25
0”
48
THE AR-15/M16
The legs are formed by bending the narrowflat portion extending from the ends of the troughdownward approximately 150 degrees, or 30degrees from the vertical. A line parallel to thebottom of the trough portion is marked 1.400inches below the trough. The mounting tabs arebent to a point where they match a flat surface.These should be sharp bends formed by a blockand hammer. The resulting tabs should be cut to
match the radius of the receiver. This can bedone in the milling machine using a large ballcutter, or it can be ground and filed to fit.
A simple fixed rear sight can be made from astrip of 14-gauge sheet metal with a leg bentupward at 90 degrees and drilled for a peep sighthole. The horizontal portion, together with thebase, is drilled and tapped for at least onemounting screw. Since this version can be better
Finished rear sight mounted in place.
Rear sight with legs bent to shape.
49
SIGHTS
served with adjustable sights, Williams or Marblesights should be used. Mounting holes for eitherof these should be drilled and tapped before thebase is attached to the receiver.
The underside of the base should be polishedto an acceptable level for finishing beforemounting. An easy way to locate the base on thereceiver in a true vertical position is to clamp thereceiver in the milling machine vise. Then, withthe mounting tabs fluxed, the base is located inposition and held by a sharp-pointed rod chuckedin the milling machine quill. The cross feed isused to move the receiver from side to side untilthe base is aligned vertically using a square orplumb bob for verification. It is then silver-soldered in place.
A military surplus M16 front sight, which isreadily available from surplus parts dealers, iseasily mounted. This should be a snug fit over
the collars left for this purpose on the barrel.Holes for the pins to secure this in place mustbe continued across the lower side of the barrelusing the existing holes in the sight base asguides. These should be cut with a 1/8-inch endmill instead of trying to drill them, since thedrill will try to drift, or crawl, to the side whereno cutting is done and likely break. These holesshould then be reamed slightly using a 9/64-inch taper pin reamer. Pins with a matchingtaper are pressed tightly in place, securing thesight in position.
An acceptable front sight assembly can befolded from sheet metal and the parts silver-soldered or welded together, but with the lowprice of the surplus sight, it is hardly worthwhile.
To avoid future problems with federal agents,it might be a good idea to remove the bayonet lugbefore finishing.
Aperture sight in place. Surplus front sight mounted on barrel.
This page intentionally left blank.
51
As stated earlier, this book was originallyintended to encompass only an upper receiverassembly and magazine adapter, which, wheninstalled on a commercial lower receiverassembly, made possible the pistol caliberconversion. But when it became likely thatfurther manufacture of commercial lowerreceivers would be prohibited when the so-called“Crime Bill” became law, existing lower receiversescalated rapidly in price. The last time Ichecked, the asking price for one of these hadgone from around $60 to more than $400. Withthis—as well as a probable scarcity—in mind, Idecided that a shop-made lower receiver wasdesirable. The design shown here is intended toconform closely to the commercial configurationand use commercial or surplus parts. Since it ismade entirely of steel, it is somewhat heavierthan the original alloy job, but it is also quite abit sturdier.
I have attempted to show here both a receivermade especially for the subcaliber conversionunit and one that will accommodate the originalfull-size, military-caliber upper receiver. Thesediffer mainly in the length of the magazineopening and the addition of the bolt hold-opendevice and original magazine latch on the full-size job. The magazine is made just long enoughto accept the pistol-caliber magazine, and themagazine latch is moved to the lower side and
just behind the opening in the same position aswith the magazine adapter used with thecommercial receiver.
I also used headless screws instead of pushpins to hold both receivers together. This not onlyeliminates the small springs and detents used inthe original, but it is more dependable. Whiledisassemby does require a screwdriver and acouple of minutes of time, it is unlikely that thegun will be rendered dysfunctional due to thepush pins being lost, as has happened in the pastwith the originals.
Construction is begun by cutting the twosheet metal parts from 12-gauge sheet metal tothe dimensions shown in the diagrams. Note thattwo sets of patterns are shown in this chapter.The one is intended for use with the pistol-caliberreceiver only and is somewhat simpler toconstruct than the other, which is intended foruse in the same manner as the full-length-magazine original.
If the .223 version is used, an offset slot mustbe formed to clear the raised magazine catchlocated on the left side of the magazine. This isdone by milling a slot .065 inch deep and .710inch wide in a piece of heavy steel plate. Thisforms the female portion of a form die. With thesheet metal panel located in position over theslot, a .500-inch-wide piece of bar stock, usedhere as a male die, is positioned on the opposite
(LOWER
RECEIVER
52
SH
OP
-MA
DE
LO
WE
R R
EC
EIV
ER
SH
OW
ING
EJE
CT
OR
LO
CA
TIO
N
Diagram #16
7.8
12
”
2.4
50
”
1.2
50
”
1.0
65
” RA
D.
1.5
60
”
1.4
50
”
.92
5”
.50
0”
53
FR
ON
T L
OW
ER
RE
CE
IVE
R P
AT
TE
RN
Diagram #17
3/8
” H
OLE
S T
O B
E W
ELD
ED
FLU
SH
DU
RIN
G A
SS
EM
BLY
2.5
00
”
2.6
25
”
2.2
50
”
88
0”
2.6
25
”
54
Diagram #18
RE
AR
LO
WE
R R
EC
EIV
ER
PA
TT
ER
N
1.2
50
”
1.2
50
”
.68
0”
5.6
25
”
55
LOWER RECEIVER
side of the sheet metal and pressed, squeezed, orhammered until the slot is formed. Thephotographs above should clarify this. While therequired slot probably could be milled into theside of the magazine well, eliminating the forming
die process, the remaining metal thickness wouldonly be some .040 inch. The formed slot willretain its original thickness of .100 inch plus,which will be considerably stiffer and stronger,making the extra work worthwhile.
One side folded around form block.Sheet metal parts are cut to size and shape.
Part is reversed in vise and the opposite side folded. Parts of rear receiver filler and stock mounting bracket.
56
LO
WE
R R
EC
EIV
ER
CO
MP
ON
EN
TS
Diagram #19
57
Diagram #20
FRO
NT
HIN
GE
BLO
CK
STO
CK
MO
UN
TIN
G B
RA
CK
ET
FRO
NT
TRIG
GE
R G
UA
RD
AN
DM
AG
AZI
NE
RE
LEA
SE
HO
US
ING
GR
IP M
OU
NTI
NG
BR
AC
KE
T A
ND
RE
AR
TR
IGG
ER
GU
AR
D
FR
ON
T L
OW
ER
RE
CE
IVE
R P
AT
TE
RN
58
THE AR-15/M16
Components clamped together for welding. Welded into single unit.
Diagram #21 FRONT HINGE BLOCK
TOP
.750” RAD.
.500”
.500”
.500”
.700”
1.00”
.450”
SIDE REAR
RELIEVED FOR WELDING
59
Both sheet metal sections are clamped againstform blocks in a large vise and formed with a heavyhammer. As I have stated before, the form blockshould be supported with blocks between the visecross arm and bottom of the form block to preventthe work from being driven downward below the
vise jaws while it is being formed with the hammer.In practice the sheet metal blank is clamped
against the form block with the material requiredto form one side projecting above the form blockand vise jaws. The side thus extending is bentdown against the form block. This done, the blank
Diagram #22
FR
ON
T T
RIG
GE
R G
UA
RD
AN
D M
AG
AZ
INE
RE
LE
AS
E H
OU
SIN
G A
ND
FIL
LE
R B
LO
CK
TOP
1.3
50
”
.88
0”
.50
0”
.97
5”
.37
5”
.12
5”
SID
E
.75
0”
RA
D.
1.1
00
”1
.20
0”
.10
0”
.25
0”
.60
0”
FRO
NT
.40
0”
RE
AR
.25
0”
.37
5”
BO
TTO
M
60
THE AR-15/M16
is turned over and again secured in the vise. Theremaining side, now extending above the vise jawsand form block, is bent at a right angle as before.Both blanks are formed in the same manner.
The formed blanks are positioned at rightangles to each other with the top edges even andin a straight line. If the short magazine version isused, three 1/4-inch holes are drilled througheach side of the magazine box part, as shown.Both parts are clamped together with the formblocks in place. The vertical seams at the rear ofthe magazine box are welded, preferably by theTIG process, and the four holes welded shut.These should be built up above the surface anddressed back flush. if this is done properly, noevidence of the welds will show.
A rectangular block, 5/8” x 7/8” x 1 1/8”, iswelded to the upper front side to form the frontmounting pin base (hinge block). This blockshould be beveled deeply on the sides adjacent tothe front face of the receiver to allow a heavy, deepweld joint. When this shop-made lower receiver iscompared to an original receiver it will be notedthat the mounting bracket, or front hinge pin baseas it is sometimes known, is quite a bit larger andthicker. This will add a small amount of weight,but it also adds quite a lot of strength, making itwell worthwhile as far as I am concerned.
A filler block is made up as shown in Diagram#22 to be welded in place at the rear of themagazine opening. The longer version is to be usedwith the pistol-caliber magazines and is made from7/8-inch material. The inside has all the metalpossible removed to save weight, and the rearportion is shaped to match the original as closelyas possible. The long magazine version is made bywelding a plate made from 12-gauge sheet metalacross the back of the magazine opening andwelding or silver-soldering a shaped filler block tothis plate. This too is shaped to match the contourof the original as closely as possible.
The welded seams should be dressed smoothand flush with the surface wherever possible.This is done prior to installing the filler block at
the rear end of the receiver so that the receivercan be mounted in the milling machine withoutinterference from protruding weld joints and thetop side milled flat. The front block is cut back tothe magazine opening with a 3/4-inch radius tomatch the upper receiver contour. A 1/2-inch slot,5/8 inch deep, is cut in the center of the frontblock to accept the front mounting pin bracket ofthe upper receiver. Both receivers should now fittogether closely. If they do not, check for highspots or burrs that are causing the interferenceand remove them.
Both receivers are clamped together and thefront hinge pin hole is drilled through themsimultaneously with a 7/32 (.2188)-inch drill(after locating and starting the hole with a centerdrill). This is followed by a 1/4-inch drill throughone side only of the lower receiver and the upperbracket. The remaining smaller hole is tappedusing a 1/4 x 28 tap. This is assuming that youwill use the headless screws instead of pins tohold the assemblies together. Otherwise youshould drill the hole completely through with the1/4-inch drill, install the spring and detent tohold it in place, and use the standard push pin.
A filler block to be installed at the extremerear of the receiver is cut from 7/8-inch steelplate to the shape and dimensions shown inDiagram #22. Here again, this part should matchthe contour of the original as closely as possible.As much material as possible should be cut fromthe inside of this part to reduce weight.
A round section, composed of the samematerial as the bolt(s) were made from, is turnedto a diameter of 1.375 inches and an overalllength of 1.350 inches. The inside is bored to adiameter of .990 and threaded with a 1.065-inch-by-16-TPI thread. This threaded sleeve is thenclamped on the top side of the filler block andwelded in place. The top edges of the filler blockshould have been beveled prior to welding,permitting a deeper, heavier weld joint. Theresulting welds must be dressed back flush withthe surface before the work proceeds further.
61
LOWER RECEIVER
Magazine rear filler. Inside is bored out to reduce weight.
Diagram #23
GRIP MOUNTNG BRACKET AND REAR END OF TRIGGER GUARD
TOP VIEW
.650”
1.250”
.430”
30˚
.100”SIDE VIEWFRONT VIEW REAR
.650” .375”
.250”
.375”
.750” RAD.
DRILL .217” TAP 1/4 x 28
62
THR
EA
D 1
.87
” X 16
1.1
00
”
1.4
50
”
.60
0”
1.2
50
”
.60
0”
1.4
50
”
WE
LD
2.6
50
”1
.05
0”
.50
0” D
IA.
.37
5” R
AD
.
.68
0”
WE
LD
1.2
50
”
1.3
75
”
BUTT STOCK MOUNTING BRACKETDiagram #24
63
LOWER RECEIVER
Ready to locate and weld in place.
When positioned correctly, magazine is a snug fit.
64
THE AR-15/M16
The front face of thecylindrical portion shouldbe shaped to the samecontour as the radiusedlower rear end of the lowerreceiver. If this receiver isintended only for use withshop-made upperreceivers, the exactcontour is not important.The only requirement isthat both parts mateclosely. If, however, it isever intended to be usedwith a commercial upperassembly, it is importantthat the 5/8-inch radiusused on the commercialpart be preserved. This canbe formed rather simplyusing a 1 1/4-inch endmill. Such end mills, witha 3/4-inch-diameter shankto allow use in the more orless standard R8 collets,are expensive and manytimes hard to find, soother methods may berequired to form it. If arotary table is available itis a fairly simple matter toform the curve required.Otherwise, a fairlysatisfactory job can bedone by roughing it toshape using the largestmilling cutter availableand finishing it with ahand grinder and/or halfround files. A hole for the tenon that keeps thestock from turning should be drilled as shown inthe drawing before this part is welded in place. Itis hard to locate and drill after installation.
To assure a close fit and proper alignment, aman drel some 7 inches long is turned to just fitinside the upper receiver for at least 5 inches. Theremainder is turned to a close fit inside thethreaded cylindrical part of the lower. Both ends
are drilled and tapped to accept 1/4 x 28 draw boltsto a depth of at least 1 inch. Large washers, bigenough to fit over each end of the receiveropenings, are required for each draw bolt.
The mandrel is installed inside the upperreceiver, and the draw bolt—with washer inplace—is screwed into the front end. The fillerblock is then pushed in place over the smallerend of the mandrel and the other draw
Mandrel is used to align parts for welding.
Mandrel is inserted in upper receiver with bracket in place on smaller end.
65
LO
WE
R R
EC
EIV
ER
Diagram #25
7.7
50
”
1.0
0”
.50
0”
1.1
00
”
1.5
40
” .90
0”
2.3
80
”
.68
0”
.50
0”
.31
2”
.85
0”
.25
0”
.40
0”
2.2
50
”
BO
TTO
M V
IEW
TOP
VIE
W, FU
LL-L
EN
GTH
MA
GA
ZIN
E
TOP
VIE
W, S
HO
RT
MA
GA
ZIN
E
66
THE AR-15/M16
bolt/washer installed and drawn up tight, pullingthe two parts together as closely as possible. Theassembly is put in place on the lower receiver andthe sheet metal trimmed to expose enough of thefiller block to assure an ample weld seam.
When this is accomplished, the front hingepin is installed and both parts are clampedtogether at the rear. The filler block is now weldedin place along both sides under the round portionand completely around the back and along thelower sides. The parts should be allowed to coolbefore the clamp, hinge pin, and mandrel areremoved to minimize any chances of warpage.
If desired, the trigger guard can be hinged ason the original, but an equally satisfactory guardcan be made by slotting the front and rear of theguard uprights and silver-soldering a sheet metalstrap in place.
Clamped in place ready for welding to lower receiver.
Welding completed and rough-finished.
67
LOWER RECEIVER
At this point all weld joints should be dressedsmooth and the entire assembly should bepolished, smooth, and free of tool marks. Nextthe assembly is secured in the milling machinevise, making certain that it is flat and level andsquare with the table. Now, using the dimensionsgiven in the drawing, the various holes are locatedand drilled. This can be done with completeaccuracy through use of the graduated dials onboth the longitudinal and cross feeds. Using thefront edge of the magazine well and the top of thereceiver as starting points, the work is moved tothe correct location for the hammer pin hole andthe hole is drilled. As usual, it should be startedwith a center drill, followed by an undersized drilland then the full-size drill. Holes drilled usingthis method are not as likely to deflect or crawl,as is common when only the full-size drill is used.The work is then moved to the correct locationfor the next hole and drilled using the samemethod. This is repeated until all are drilled. Aslot is cut in the location shown for the triggerand a hole for the grip bolt drilled and tapped.
Rear guard welded in place.
Bottom view of rear trigger guard.Rear trigger guard and grip mount.
68
Diagram #26
6.3
75
”
.32
5”
2.1
00
”
2.0
0”
3.3
55
”
.62
5”
.85
0”
.94
5”
1.1
32
”
.32
5”
2.0
50
”
.71
7”
LO
WE
R R
EC
EIV
ER
HO
LE
LO
CA
TIO
NS
69
Diagram #27
30
˚
2.3
00
”2
.38
0”
LO
WE
R R
EC
EIV
ER
WIT
H F
UL
L-L
EN
GT
H M
AG
AZ
INE
70
THE AR-15/M16
While the operationsdescribed may seem time-consuming and compli -cated, it isn’t actually asdifficult as it may seem.Such a receiver willrequire a full day’s work tobuild from start to finish,but if one wants one badenough and this is the onlyway to get it, it will beworthwhile.
Again, be advised thatthis part may be illegal tomanufacture. Think care -fully and weigh the conse -quences before you buildone. Mine was madebefore the so-called“assault weapons” banwent into effect and istherefore considered legal.But since the law is now ineffect, I wouldn’t beinterested in buildinganother. The requirementthat home-manufacturedfirearms be marked withthe maker’s name, address,and a serial numbershould also be kept inmind.
Completed lower receiver with pistol version upper pinned in place.
Lower receiver with open bolt plug partially inserted.
Same, with breech plug in place.
71
LOWER RECEIVER
Clamping pressure can be exerted using sturdy vise with exten -sion on vise handle. Don’t try this with a cheap import vise.
Offset partially formed, further clamping pressure will finish.Male and female dies used to form offset in left receiverwall of full-length magazine opening.
View of offset, formed as shown.
This page intentionally left blank.
73
For years many of us used Sten magazines inour experimental assault-type firearms, mainlybecause they were plentiful and cheap.Apparently they are still plentiful, although theprice has gone up.
While the existing magazines should probablybe used as long as they are available, mainly tosave labor, an alternate source of supply shouldbe kept in mind. This means making themyourself. Although I have detailed a method formaking them in other books, a different method,which is somewhat easier but equally satisfactorywhen properly done, is described herein.
It should be pointed out that this unit wasoriginally designed as a 9mm conversion only, tomate with existing AR-15 or M16 lower receiverassemblies. The Sten magazine is the correctwidth to just fit inside the original magazine well,and, when used in combination with themagazine adapter described in the small partschapter, allows a close, snug fit. If the unit isbuilt in one of the 10mm calibers or .45 ACP, thesame outside dimensions must be adhered tosince wider magazines, such as the Thompson,grease gun, and the like, will not go in the hole.
The same Sten magazines as used in the 9mmcan be used with the larger calibers if the insideis simply swaged slightly longer to permit feedingof the longer cartridges. The maximum overalllength of the .45 ACP cartridge is stated to be
1.275 inches, and that of the 10mms is somewhatless, depending on which one is used. All that isrequired is to swage the concave seam at the rearof the magazine body slightly flat, therebylengthening the inside of the body withoutincreasing the outside length.
The swage used to accomplish this is madefrom a flat bar of steel 1.300 inches wide, .312inch thick, and 11 inches long. The .312 (5/16)-inch width is to permit the swage to pass betweenthe magazine lips. The 11-inch length is to alloweach end of the swage to extend from the body sothat each end can be supported on blocks whileany deformation caused by the swaging operationis restored to its original shape using a block andhammer. The end intended to enter the magazinebody should have a short bevel on all four edges.
In use, the swage should be lubricated withheavy grease and started into the bottom end ofthe magazine body. A steel spacer, .187 (3/16)inch thick and 1 inch wide, is positioned on eachside of the swage to keep it in place under theseam. It is forced into the magazine body by lighthammer blows. When completely through andextending past the feed lips, the swage issupported at each end by steel blocks and theback side restored to its original flat shape using ablock and hammer. The magazine lips must bespread open slightly to facilitate feeding of thethicker cartridge. This is accomplished using
(MAGAZINES
74
MA
GA
ZIN
E F
OR
M B
LO
CK
Diagram #28
BA
CK
SID
E
SID
E VIE
W
.50
0”
.65
0”
1.4
”
10
”.7
30
”
.36
0”
.50
0”
.24
0”
.24
0”
.25
0”
15
˚
.25
0”
2.2
”
.25
0”
.25
0”
RE
AR
EN
D VIE
W
1/4
” HE
MIS
PH
ER
ICA
L SLO
T, CU
T WITH
BA
LL CU
TTER
CA
RTR
IDG
EG
UID
ES
, CU
TW
ITH 1
/4”
BA
LL CU
TTER
75
Diagram #29
MA
GA
ZIN
E B
OD
Y P
AT
TE
RN
9.5
00
”
.74
0”
.10
0”
.50
0”
4.5
40
”
1.4
00
”
9.2
50
”
76
THE AR-15/M16
pliers or vise grips and is more or less a trial-and-error operation.
Sten magazines reworked in this fashion willhold eighteen to twenty .45 rounds or twenty-three to twenty-five rounds of 10mm ammu -nition. Lesser-capacity magazines can be made bycutting and reducing the length of an originalmagazine and rebending the flanges at the bottomfor the floorplate to slide over. Needless to say,the follower spring is shortened by acorresponding amount. The follower legs can beshortened by as much as 3/4 inch with no illeffect, thus allowing a shorter magazine whileretaining a larger capacity.
New magazines can be manufactured bymaking up a form block and bending the sheetmetal body around it. The form block should be1.400 inches deep, .730 inch wide and 10 incheslong. This can be made from a solid bar or fromthinner strips welded or riveted together. It is afairly simple matter to reduce a bar of 1 1/2” x3/4” material to size, just as it is to fasten three
1/4” x 1 1/2” strips together and cut them downin the same manner. The corners on the frontside should be rounded to approximately a 1/8-inch radius. The rear corners should be fairlysharp, radiused only slightly. A convex slot is cutalong the centerline on the back side of the block.This slot should have a .125-inch radius and canbe cut with a 1/4-inch ball-cutting end mill to adepth of .100 inch if for a .45 magazine and .150inch if intended for a 9mm. The end that willform the top, or lip end, should be cut at a 5-degree angle by 1/2 inch long.
Two more concave grooves with a .125-inchradius must be cut on each side at the top asshown in Diagram #30. These form guide ribs,which will assist in the reduction of thestaggered, near double-row magazine to thesingle-row feeding, which, at least in my opinion,is far superior to a double-row feed. A 1/8-inchhole is drilled on center near each end and on thefront side of the block, and close-fitting guidepins are installed.
Groove is cut on rear side of form block using ball cutter. Cuts to form guide ribs are made with same ball cutter.
77
UP
PE
R R
EIN
FO
RC
ING
JA
CK
ET
FL
OO
RP
LA
TE
Diagram #30
3.0
0”
1.2
50
”
.80
0”
1.2
50
”
2.7
00
”
1.0
50
”
1.6
80
0”
.50
0”
1.3
00
”
78
THE AR-15/M16
It will be noted that the sides of originalfactory-made magazines have a slight tapertoward the front. This is omitted with the shop-made units since the taper is difficult to formusing the method described here. If the guide ribsand magazine lips are formed correctly, nodeleterious effect will result.
A blank is cut from 20-gauge (.032-inch)sheet metal to the dimensions shown with acenterline marked lengthwise. Correspondingholes to fit over the guide pins in the form blockare drilled on the centerline. The blank is nowmated to the block and the assembly clamped inthe vise with the front and back surfaces betweenthe vise jaws and the upper side of the block evenwith or slightly above the vise jaw. The undersideshould be blocked up using spacer blocksbetween the vise throat and bottom of the block.The protruding sheet metal is bent flat againstthe form block using a hammer and flat bar ofmetal. The assembly is then turned over and theother side bent flat in thesame manner. An addi -tional spacer must beadded at the back for thislast side to clear thepreviously bent side, whichnow extends past thesurface of the block.
Form block and sheet metal blank are clamped in vise.
Template can be cemented to sheet metal as a guide tocutting magazine blank.
79
MAGAZINES
Sides are folded using block and hammer. Rear sides are folded and formed using hammer andswage.
Seam is silver-soldered while clamped around form block.
80
THE AR-15/M16
The assembly is next turned with the frontside down and again clamped in the vise and oneside bent flat. The edge of this side is swaged into the half round slot using a hammer and therounded edge of a 3/16-inch-wide steel block.The remaining side is given the same treatment.At this point the seam is welded or silver-soldered. The magazine lips are bent flat againstthe form block and the guide ribs formed usingthe same 3/16-inch swage and hammer.
The upper “jacket” or collar is cut from thesame 20-gauge sheet metal and mounted inplace. If a number of small 3/16-inch holes aredrilled through the sides of the jacket, the jacketcan be welded to the body through these holesand the welds dressed flush. A neat appearance isthus preserved. The seams at the upper cornerswhere the magazine lips are formed are alsowelded and the welds dressed flush.
A flange is bent outward at a right angle to thebody at the bottom edge of each side. These are tohold the floorplate, which iscut from the same 20-gaugesheet metal and the edgesbent to slip over the flanges.A hole to accept a pin thatkeeps the plate in place isdrilled as shown in Diagram#30. The retaining strip,consisting of a 20-gaugesheet metal strip with bothends bent upward 90degrees, is fabricated, and ahole corresponding to theone in the floorplate isdrilled and a close-fitting pinsilver-soldered in place. Thisserves to hold the floorplatein place except when the pinis pushed inward againstpressure exerted by themagazine spring, which willallow the floorplate to bemoved forward off themagazine. This permitsremoval of the magazinespring and follower.
While it is possible to
Rear sides are folded and formed using hammer andswage.
Upper jacket welded in place.
Upper jacket in place on magazine body.
81
MAGAZINES
Component parts of factory magazine.Lower end showing cover plate in place.
Magazine with cartridge in place, ready for feeding.Upper end of magazine showing double wall thickness.
82
THE AR-15/M16
bend a magazine spring to shape using pliers, amuch neater job will result when it is woundaround a mandrel. This is accomplished byrounding the edges of a 3/8” x 1” steel bar, 14inches long. A hole is drilled through the side atone end to accept .065-inch-diameter springwire. The resulting mandrel is chucked in thelathe with the opposite end supported by the tailstock center. A V-shaped groove is cut across thefaces of two small blocks that are clamped in thetool post. In practice, one end of a length of.065-inch-diameter music wire is passed throughthe V grooves of the tool post blocks and theextending end inserted in the hole in themandrel. The tool post is tightened to exerttension against the wire as it is drawn throughthe notches. With the lathe running at theslowest speed and set for the coarsest thread
available, the spring is wound. The factory springis approximately 13 inches long and consists of26 coils spaced 1/2 inch apart. This should beduplicated as closely as possible.
The follower is made with a top sectionshaped as shown in Diagram #31, with a legwelded to each end. The magazine is assembledby first inserting the follower into the bottomend. The spring is then put in place, followed bythe retaining strip. This retaining strip isdepressed against the spring, and the floorplate isslipped over the flanges and pushed to the rearuntil the retainer pin snaps in place.
It is hoped that commercial magazines remainavailable and plentiful. If not, however, this neednot present a major problem since, as can be seenhere, satisfactory magazines can be made in thehome workshop if necessary.
MAGAZINE FOLLOWERDiagram #31
WELD
2.700”
.100”
1.250”
2.200”
.625”
83
If an original lower receiver is used, a spacer,or filler block, which also serves as a mountingpoint for the magazine latch as well as the ejector,must be used. This part also serves to adapt themagazine opening to the size required to containthe smaller pistol cartridge magazine.
The block proper should be made fromaluminum, not only to save weight but because itis also easier to machine than steel (usually).This part should fit the magazine opening closely.While approximate dimensions are given in inDiagram #32, these may not be anywhere closeto the actual size required to fit your particularlower receiver since different manufacturers usedifferent dimensions. This was the primaryreason my commercially produced conversionunits were not as successful as they should havebeen. If I made the filler block to maximumdimensions, my customers complained becauseof the work involved in filing them down to fit.On the other hand, if this part was made to fitthe smaller, tighter opening found in anotherbrand of lower receiver, enough sideways travelwas introduced to prevent the ejector fromworking. So make this part to fit snug inside yourmagazine opening, so that it requires a slighteffort to push it into place.
With the part properly fitted and in place, aslot for the original magazine latch to engage andhold this part in position should be marked
through the existing slot in the lower receiver andcut with a 3/16-inch end mill.
A slot to accept the ejector is cut using a 1/8-inch end mill at the location shown in thedrawing, and the ejector is cut to shape from 10-gauge flat stock. With the ejector in place, two3/32-inch holes are drilled through both the blockand the ejector simultaneously at the locations
(SMALL PARTS
Magazine adapter for use with commercial receiver.
84
MAGAZINE ADAPTOR COMPONENTS
EXTRACTOR FORMED FROM .125”HEAT-TREATABLE FLAT STOCK
NOTE: COMMERCIAL RECEIVERS VARY INDIMENSIONS. THE DIMENSIONS SHOWNARE APPROXIMATE. ADAPTOR MUST FITMAGAZINE OPENING CLOSELY.
.500”
.500”
.500”
.150”
.600”
.200”
.400”
2.600”
2.600”
.300”
1.150”1.00”
Diagram #32
85
MA
GA
ZIN
E A
DA
PT
OR
US
ED
WIT
H C
OM
ME
RC
IAL
LO
WE
R R
EC
EIV
ER
.25
0”
.50
0”
.50
0”
.50
0”
.95
0”
.85
0”
.84
0”
1.5
00
”
.25
0”
.95
0”
2.3
50
”
.75
0”
.25
0”
.20
0”
2.4
50
”
.85
0”
RE
AR
SID
E
FRO
NT
BO
TTO
M
TOP
.12
5”
Diagram #33
86
Diagram #34
MA
GA
ZIN
E L
AT
CH
, SH
OP
-MA
DE
RE
CE
IVE
R
.12
5” S
PR
ING
GU
IDE
SILVE
R-S
OLD
ER
ED
IN P
LAC
E.
.50
0”
.55
0”
.60
0”
.65
0”
.40
0”
.20
0”
.12
5”
SID
EFR
ON
T
.25
0”
2.7
00
”
RE
AR
.12
5” D
IA.
.98
0”
87
shown, after which close-fitting pins are pressedin the holes to hold the ejector in place.
The magazine latch is cut to shape from 1/4-inch flat stock. The slot and spring pocket aremilled in the front face of the block, and the pivotpin hole is drilled through both parts—again,simultaneously. The latch should be made slightlylonger than shown in Diagram #34 to allow forproper fitting during assembly.
It should be obvious that if the shop-madereceiver with the short magazine opening is used,the filler block is not used and the alternatemagazine latch shown is used instead. The samesheet metal ejector is used; however, the slot toaccept it is milled into the receiver and the partsilver-soldered in place.
Component parts used in adapter.
Adapter in place. (Note that original magazine latch limitsdepth of magazine insertion.)
Rear receiver-mounting bracket.
SMALL PARTS
88
THE AR-15/M16
When the pistol version is built, a plug, orcap, should be made up to screw into the receiveropening, taking the place of the butt stockmount. If used as an open-bolt version, a singlerecoil spring guide is mounted in the center ofthe cap. This is done by drilling a 1/4-inch holethrough the center of the cap and silver-solderinga suitable length of 1/4-inch drill rod in place.The inside of this cap is bored out, as shown inthe drawing, to reduce weight. The knurled bandon the largest diameter flange not only adds tothe overall appearance but provides a grippingsurface to aid in installing or removing the part.
When used as the closed-bolt version, thecap is made to the same overall configurationand dimensions except that the recoil springguide is omitted. This version requires the sameguide, made for two springs, as used in the short-bolt rifle version. This one is made by drillingtwo .156-inch diameter holes, which match thewidth of the spring holes in the bolt, through athin plate of 3/16-inch flat stock. The ends oftwo matching lengths of 5/32-inch-diameter drillrod are inserted in these holes and silver-soldered in place.
In my prototype gun, I used two military M1Carbine action springs in the closed-bolt version.
These are too long in their original state and mustbe cut off, a little at a time, until the bolt willopen far enough to pick up cartridges from themagazine. I cannot tell you exactly how longthese springs should be since varying dimensions,such as the depth of the holes in the bolt, andvarying thickness of the wire used in the springswill have an effect.
For the open-bolt version, I used a springobtained from an auto parts store. This onemeasures .375 inch in diameter, is wound from.050-diameter wire, and was originally 7/12inches long. This one too was shortened, a littleat a time, until the action would open completely.As with the closed-bolt version, this is strictly a“cut and try” proposition.
Extractors are identical for all three versions.Each should be cut from a better grade ofmaterial than common sheet metal, due to thefact that the hooked end must jump over the rimof each and every cartridge fed through the gun.Needless to say, if soft material is used the partwill wear and deform rapidly. Leaf spring materialcan be milled to the required 1/8-inch thickness,or a thin slice can be cut from the end of an axle.Do not neglect this if you expect to use the gunextensively. As with most other small parts, this
Breech plug used in open-bolt pistol version.
Diagram #35
EJECTOR, SHOP-BUILT RECEIVER
.600”
.150” .500”.300”
.750”
.500”
1.400”
89
SMALL PARTS
part should be made slightly oversize and dressedto exact fit during assembly.
If the closed-bolt configuration is adhered to,commercial firing mechanism components, whichinclude a hammer, trigger, disconnector, safety,and necessary springs, are available fromcommercial and surplus parts sources. These areavailable at attractive enough prices to make itmore sensible to buy them than to build them.Unfortunately, several of the surplus partssuppliers got the idea in their heads that theycould rip off consumers by doubling, orsometimes tripling, the price of these small partswhen the assault weapons ban went into effect.This, of course, didn’t work out since there weremany more such parts available than there wasdemand for them. As a result, prices have againreturned to normal and should remain so foryears to come. An example of this is that allrequired firing mechanism parts can be obtainedfrom dependable parts suppliers such as QualityParts Co. in Windham, Maine, for around $40.These are new parts, and Quality Parts shipspromptly, without any B.S. or excuses.
Diagram #36
Diagram #37
RECOIL-SPRING GUIDES, CLOSED-BOLT VERSION
EXTRACTOR SAME FOR BOTH BOLTS
.156” DIA. SPRING GUIDES
.200”
1.050”
.650”2.700”
1.100”
.800”.300”
.100”
.300”
.250”
45˚
MADE FROM .125” THICKNESS, HEAT-TREATABLESTEEL. HOOK SHOULD BE MADE OVERSIZE AND FITTEDTO SNAP OVER THE CARTRIDGE RIM DURINGASSEMBLY.
.087” PIVOT PIN HOLE SHOULD BE DRILLED THROUGHBOLT AND EXTRACTOR SIMULTANEOUSLY.
.800”
90
THE AR-15/M16
The open-bolt version will require manu -facture of a sear, trigger, and disconnector. Theseare designed to interchange with the closed-boltparts, using the existing pivot pins and pin holes,with no change in the lower receiver. This systemuses a combination trigger bar and disconnector,which is hinged to the sear. The lower end of thispart engages a projection protruding from theforward end of the trigger. Consequently, whenthe trigger is pulled to the rear the sear is pulleddownward, out of engagement with the bolt,allowing the bolt to travel forward, pushing acartridge from the magazine into the chamber. Atthe forward end of the bolt stroke, the firing pin
crushes the primer, causing the round to fire. Atthis point, a combination of recoil and gaspressure causes the bolt to move to the rear,ejecting the fired case in the process, where it isagain caught by the sear and held in therearward, or cocked, position until another pull ofthe trigger causes the cycle to be repeated. The“lump,” or projection, at the top of the trigger baris depressed by the forward-moving bolt, whichmoves the lower, hooked end of the bar out ofengagement with the trigger. This requiresallowing the trigger to move forward again beforea subsequent shot can be fired.
TRIGGER (OPEN BOLT)Diagram #38
.156” DIA.
.400”
1.100”
.175”
.800”.125”
.125”
.250”
.450”
1.250”
.500”
.375”
.700”
1.950”
91
SEAR (OPEN BOLT) Diagram #39
DETENT MADE FROM .187 DIA. DRILL ROD
1.500”
.100”
.187”
.125”
.300”
.850”
.400” .400”.200”
1.150”
.640”
.600”
.450”
.200”
.200”
.350”
.156” DIA.
SPRING POCKET .250” DIA., .300” DEEP
92
THE AR-15/M16
Full automatic fire is achieved by pulling thetrigger farther to the rear, against the pressureexerted by the U-shaped wire spring located atthe rear of the trigger. This causes the forwardend of the trigger to contact a projection locatedon the lower end of the sear, which, if the triggeris held back, holds the sear out of engagementwith the bolt, allowing it to move forward andback unimpeded. This causes full automatic fire.
The sear is cut from 5/8 (.625)-inch-thicksteel plate. This must be of a type that is shock-resistant and capable of heat treatment. As usual,4140 or 4340 will serve admirably for this. Notethat the disconnector spring bears against the
pivot pin, providing friction to hold it in place.The disconnector spring is 3/16 inch in diameter,wound from .018-inch wire, and theuncompressed length is between .300 and .400inch. The sear spring, located in the lower frontside, can be a section cut from the M1 Carbinerecoil spring used in the closed-bolt version.
The trigger is made from the same materialwith a projection at the forward end on the rightside to engage the trigger bar/disconnector. Twosmall 1/16-inch-diameter holes are drilled in thelocation shown to accept the U-shaped wirespring, which is formed from .065-inch musicwire. This spring bears against the lower side of
TRIGGER DRAWBAR AND DISCONNECTORDiagram #40
1.0”
.250”
.125”.750”
.150”
.100”
1.250”
.250”
PIVOT-PIN HOLE IS.087” IN DIAMETER.
THIS PART IS MADE FROM .125-INCH-THICKNESS,HEAT-TREATABLE STEEL. IT SHOULD BE MADESLIGHTLY OVERSIZE AND FITTED DURING ASSEMBLY.
93
RE
LA
TIO
NS
HIP
AN
D P
LA
CE
ME
NT
OF
OP
EN
-BO
LT
TR
IGG
ER
PA
RT
S
Diagram #41
94
THE AR-15/M16
the safety shaft, providing resistance to rearwardmovement of the trigger after the first, orsemiautomatic, stage.
The trigger bar should be made from similarmaterial, except that it is only 1/8 inch thick.Both the hook at the bottom and the lump at thetop should be left slightly oversize to allow fittingduring assembly.
For use in the closed-bolt version, an originalfiring pin can hardly be improved on. Here again,one can be purchased for less than the cost to
make one. A drawing is included, however, in theevent that manufacture should be required. Drillrod will suffice as material for this. Stems fromautomobile engine valves or shock absorber shaftscan also be used. The experienced lathe operatorwill know to use a sharp cutting tool, set exactlyon center, taking light cuts. Those who havenever done this before may gain some valuable,although unpleasant, experience when making apart such as this.
FIRING PINDiagram #42
.625”2.00”
.250”
.575”
.375”
.125”.100”
.150” DIA.
.125” DIA..065” DIA.
.100”
3.285”
95
Before heat-treating and final finishing areperformed, the parts should be assembled andany further fitting done as needed.
Assembly of the upper unit is begun byinserting the barrel tenon into the forward end ofthe upper receiver and screwing the barrelshroud, or fore-end, in place, which, whentightened against the flange of the barrel, holds itin place. The front sight is put in place and theretainer pin holes enlarged with a 3-0 taper pinreamer. Corresponding taper pins can be turnedfrom 3/16-inch drill rod. Actually, it is a fairlysimple matter to form the taper on these with aflat file while spinning each in the lathe. Thesepins are not installed permanently until afterfinal finishing.
The firing pin and return spring are insertedin the bolt and the retaining pin installed. Firingpin protrusion should be .055 to .060 inch. Thiscan be checked by holding the base of the firingpin flush with the bolt slot and measuringprotrusion from the bolt face with a depthmicrometer or vernier caliper. A 3/16-inch-diameter coil spring wound from .018-.022-inch-diameter wire is placed in the spring pocket,followed by the extractor, which is pinned inplace. The spring must be short enough to allowthe extractor hook to snap over the cartridge rimwhile retaining enough tension to hold it againstthe bolt face. It is a good idea to start with a
longer spring than necessary and cut it off, a coilat a time, until it works the way it is supposed to.The outer surface of the extractor body should beflush with, or slightly below, the surface of thebolt body. The front tip must not rub against thebarrel slot.
The assembled bolt is now pushed in placethrough the rear of the receiver until the hole forthe cocking lever lines up with the receiveropening, allowing the cocking lever to be put inplace. The recoil springs are placed over theirrespective guides, and the assembly installed withthe springs in their corresponding holes in thebolt. The unit is now ready for installation on thelower receiver.
The open-bolt pistol version is assembled inthe same manner except that the fixed firing pinis already in place and requires no assembly, andthe single recoil spring and guide are used.
Lower receiver parts are assembled inidentical fashion in both the commercial and themanufactured versions, except that the magazineadaptor must be used in all commercial versionsand those of the manufactured version having afull-size magazine opening. The smaller magazineopening version requires only that a small coilspring (a short length of the carbine recoil springworks well for this) be placed over the springguide and the latch pinned in place. Thetrigger/disconnector and hammer are pinned in
(FITTING ANDASSEMBLY
96
THE AR-15/M16
place and the safety installed. There should be nofunctional problems with the firing mechanismwhen used in the commercial version. Assumingthat the pivot pin holes were drilled in the exactlocations specified, the manufactured versionshould work equally well. If, however, you did notadhere closely to the locations shown, (remember,I warned you about this earlier), all sorts ofproblems may result.
If the hammer and trigger pins are too farapart, the disconnector quite likely won’t work.This can usually be corrected by building up theforward ends of both the trigger and disconnectorslightly by welding and reshaping them. If theholes are too close together, the hammer will notremain in the cocked position and/or thedisconnector will not release the hammer. Thiscan usually be corrected by shortening the triggernose and/or the disconnector where it engagesthe hammer notch. This will only work if only aslight variation exists. Otherwise, the easiest outwill be to weld up the holes and redrill them—inthe right place this time.
The open-bolt trigger assembly is installed byfirst pinning the trigger in place, with the tail endof the U-shaped spring bearing against theunderside of the safety. This spring causes extraresistance as the trigger is pulled farther to therear, causing a definite step between the fairlylight first stage, or semiautomatic, pull and theprogressively harder second stage, whereby whenthe trigger is pulled farther to the rear, fullautomatic fire is accomplished. The originalsafety, as used in the closed-bolt version, isinoperative in this instance.
With a short length of 3/16-inch-diameter coilspring, wound from .016- to .020-inch wire,placed over the detent and installed in the springpocket, the trigger bar/disconnector is put inplace through the slot in the trigger and pinned.A short length of coil spring, cut from the excessportion of the carbine recoil spring, is placed inthe spring pocket at the lower front of the searand the sear is pinned in place. A small amountof wheel bearing grease deposited in springpockets such as this will keep the springs fromfalling out while the part is being installed—notonly in this instance, but many others as well.
With the parts in place, the hook at the lowerend of the trigger bar must move forward underthe projection at the front of the trigger. If thisdoesn’t happen, material must be removed fromeither the hook or the trigger until it does. Thelump at the top of the trigger bar will also requirefitting at this point. As the bolt moves forward,the full-diameter portion rides over and depressesthis lump, which, in turn, moves the hook at thelower end out of engagement with the trigger.This disconnects it, allowing the sear to engageand hold the bolt at the end of its rearward travel,even though the trigger is still held to the rear.The trigger must be released and allowed to moveforward before a second shot can be fired.
When the trigger is pulled farther to the rear,the front edge engages a ledge at the bottom ofthe sear and holds it out of engagement with thebolt. This causes full automatic fire. It isdesirable that the trigger have at least 1/8 inch offree travel between the point where it disconnectsand the point where the sear ledge is depressedby the trigger nose. This is obtained by removingmaterial from either the lower side of the triggernose or the upper side of the sear ledge.
After the grip and butt stock are added (ifassembled as a rifle), both receivers are joined byfirst pinning both together with the front hingepin. The rear mounting bracket is inserted in therear of the upper receiver and the rear pininstalled. When used as the pistol version, thereceiver cap, or plug, together with thecorresponding recoil spring, is threaded in placein the rear of the receiver assembly instead of thebutt stock.
The action should be cycled by hand severaltimes, and if binding or excessive friction ispresent, the cause should be identified andeliminated. Proper functioning of the dis -connector should be checked by hand-cycling theaction with the trigger held back. The hammermust not fall or the open bolt move forward at theend of each cycle until the trigger is released andpulled again.
If you have built both versions, the closed-bolt assembly should be used to check for properfeeding. If only the open-bolt version is made up,a few dummy cartridges, consisting of a bullet
97
FITTING AND ASSEMBLY
seated in a sized case and without powder orprimer, should be used. If live rounds are used totest feeding in this version, they will fire when thebolt slams closed.
With a s ingle round in place in themagazine, the bolt is retracted and allowed toslam forward unimpeded, just as it would inactual f ir ing. The cartr idge should feedsmoothly into the chamber, and when the boltis again retracted, the cartridge should bewithdrawn from the chamber and ejected as thebolt nears the end of its rearward travel. If thecartridge does not feed properly, try letting thebolt go forward slowly, observing where thebullet encounters interference. If it hits belowthe barrel approach cone, the magazine lipsshould be spread open slightly, allowing thecartridge to rise slightly higher in the magazine.If it strikes too high, the forward ends of thelips should be bent inward slightly. If the bulletnose hits on either side, move the lip on thesame side inward slightly and the opposite sideoutward a like amount. It should be stated,however, that when a new magazine and theangled approach cone system detailed here areused, feeding problems are seldom encoun -tered. If the single round feeds and ejects in themanner expected, the action should be cycledwith three or more rounds in the magazine andadjustments made if required.
Close attention should be paid to headspacing, especially if the firearm is to be usedextensively. Although a blowback action, as usedhere, can probably be fired safely with eitherinsufficient or excessive head space, problemsmay occur further down the line. For instance, ifthe chamber is even as little as .010 inch short ofbeing deep enough, the forward end, or mouth, ofthe case, which is what stops forward movementof the cartridge in the chamber, will slam againstthe end of the chamber with considerableviolence. It is possible that the case may batter ordeform at the mouth, which could pinch thebullet, raising chamber pressure to a dangerousdegree. The chambered cartridge should havefrom .003 to. 008 inch of clearance (head space)between the cartridge head and the bolt face.
Conversely, if the chamber is too deep,misfires may occur and case heads may separatefrom the bodies. It should also be noted that ifthe chamber is cut too deep, even as little as .020inch, the gun will probably not fire at all,especially in the open-bolt version. The fixedfiring pin simply does not indent the primer deepenough to crush it.
I am aware that in recent times certainpseudo-experts have expounded a theory of“advanced primer ignition,” whereby, as they tellit, the cartridge in the process of beingchambered is slowed by friction to a point wherethe firing pin ignites the primer before the actionis completely closed. This is supposed to serve asa sort of hesitation lock, delaying the opening ofthe action. This is pure and simple conjecture ontheir part, since, in actual practice, the cartridgemust come to a positive stop before the firing pincan impact the primer with sufficient force anddepth to detonate it. This simply won’t work in afirearm of this type.
I learned the truth of this several years agowhen I was actively engaged in building andmarketing an open-bolt 9mm assault pistol. Oneof my employees was assigned the task ofchambering the barrels. This should have been afairly simple, straightforward task since thechamber reamer was fitted with a stop collar,which should have limited the depth of the cut.Some way, however, my man managed to cut thechambers approximately .030 inch too deep.When these barrels were used on assembled gunsand test-firing was attempted, not a single one ofthem would fire. I was required to remove a likeamount of metal from the front of the bolt bodiesof each of the affected guns, which let the boltsmove forward far enough to take up the excessivehead space. This proves, to me at least, that thetheory of friction slowing the case to a pointwhere “advanced primer ignition” occurs is justthat—a theory, which doesn’t work.
Once the gun is assembled and tentativelyworking the way it should, it should bedisassembled and final polishing and heat-treating of parts requiring it should be performedbefore actual firing is attempted.
This page intentionally left blank.
99
The bolt, as well as the sear, trigger, andtrigger bar for the open-bolt version, should beheat-treated. This is done primarily to preventbattering, or deformation, and rapid wear.Commercial parts obtained from reputablesources are already heat-treated and require nofurther attention.
Since I have discussed the principles of heattreatment in several other volumes, there is littlepoint in repeating it here. All that is required is tothoroughly heat the steel parts to a temperatureslightly above their critical stage, followed bycooling them quickly by plunging them into aquenching bath consisting of water, oil, brine, orother liquid as specified. Correctly done, this willresult in a part (or parts) with a surface so hard afile won’t touch it. It is also extremely brittle inthis condition—so much so that even a smallamount of shock may crack or break it. Thiscondition is remedied by once more heating theparts to between 300 and 1290 degrees andallowing them to cool slowly. The exacttemperature required for this “drawing,” or“tempering,” will vary considerably, depending onthe composition of the steel, the carbon content,and the hardness desired.
The bolt(s) in this project should be heat-treated simply to prevent battering ordeformation. Since this is a blowback action thatis never actually locked, shear strength is not a
determining factor. If commercial 4140 or 4340is used for this, the heat treatment is fairlystraightforward. The part should be heated tobetween 1450 and 1550 degrees, held there longenough to be certain that the part is completelysaturated with a uniform temperature, andquenched in a bath of SAE #10 nondetergentmotor oil (or similar) which is at or slightly aboveroom temperature. This should result in a surfaceso hard that a file will simply skate across itwithout cutting. This, of course, would be idealfor wear resistance. However, any contact pointssubject to even a small amount of shock wouldsoon crack or break. So, we must draw thetemper at a temperature of approximately 800degrees, which will soften it slightly but also putquite a bit of toughness back into it. This is doneby again heating the part to the specifiedtemperature and allowing it to cool slowly. If nospecific temperature control is present, the partshould be heated until it passes through a darkblue color and begins to turn green, at whichpoint it is allowed to cool.
If using axle material or similar, you probablywon’t know the exact composition of the steel, soa bit of experimenting may be required. A scrap ofthis same material is used for testing, and sincemost medium- and high-carbon steels requireheating to between 1450 and 1650 degrees forhardening, try heating the scrap to a bright,
(HEAT-TREATINGAND FINISHING
100
THE AR-15/M16
Small parts to receive heat-treatment are tied to heavywire . . .
Then temper is drawn by polishing bright, heating on steelplate.
. . . and quenched when desired color (usually brightcherry red) is reached.
. . . heated to proper color . . .
101
HEAT-TREATING AND FINISHING
glowing, cherry red and quenching it in the oilbath as described above. It should now be glasshard. If it is not, try the same, or another, scrap ata slightly higher temperature, and when theproper combination is found, apply it to the partto be hardened.
The small parts requiring same should betreated in similar fashion, except that they shouldbe drawn at approximately 600 degrees. This isindicated by a dark blue color.
As I have stated in previous volumes, since Ihave no control over anyone’s attempts at heattreatment other than my own, I cannot accept anyresponsibility for problems you may encounter.
With the heat-treatment done to yoursatisfaction, final polishing of all component partsshould be done.
A dull, flat black finish is usually considereddesirable for a paramilitary firearm of this type.When the upper assembly is used in connectionwith the commercial lower, such a finish willusually be similar to the anodized black finishused on the aluminum parts.
To obtain such a finish, the parts need not bepolished to the degree required to obtain thebright blue finish used on sporting arms. Even so,all scratches, tool marks, and other blemishesshould be removed. This can be done with powerpolishing equipment or by hand using files andabrasive cloth.
When the hand-polishing method is used,tool marks and blemishes are removed with afile. The round parts can be rotated in the latheand tool marks removed by holding the fileagainst the spinning part and moving it back andforth. This is followed by progressively finer gritsof abrasive cloth, up to a final treatment with320-grit wet or dry paper. This will be adequatefor the finish used here. Flat parts are given thesame file and followed by the same abrasivecloths wrapped around the file, wood blocks,dowels, or whatever it takes to contact and polishall exposed surfaces.
Following this, all exposed surfaces aresubjected to a bead blast or sand blast treatment,which gives the metal a slightly roughened,frosted surface. Most machine shops andautomotive paint and body shops have the
equipment to do this, and most will do it for anominal charge.
Following this, the parts are degreased usingone of the degreasing or detergent solutionsfound in grocery, paint, and hardware stores. Amild lye and water solution can also be used forthis. After boiling for a few minutes in one ofthese solutions, followed by rinsing in clear water,they are ready for the bluing process. The partsshould no longer be handled with the bare hands,since even the slightest smear of oil from yourhands may have an adverse effect on the coloringprocess. Rubber gloves should be worn, or metalhooks or wires should be used to hold the parts.
In previous volumes I have describednumerous methods and formulas used to impartthe color desired. Any of these would be suitablefor this project. Most of them have seriousdrawbacks for the one-time gun finisher in thatthey require either extensive equipment or aconsiderable amount of time to perform. In thisbook I will describe a couple of processes thatmay be useful when only a few parts are involved,since they require only a small outlay formaterials and no equipment whatever.
One of these solutions is made by using asmuch copper sulfate—which is a bluishcrystalline powder also known as bluestone orblue vitriol and available from drugstores—as 4ounces of distilled water will dissolve. Fifteen totwenty drops of sulfuric acid should be added tothis. The resulting solution is swabbed on thepolished parts, which causes a copper platingaction. A second coat will thicken the platingslightly. This is followed by a coat of sodiumthiosulfide, which is used in processing film andcan be found at photography stores. This will turnthe copper black. Arsenic tri-oxide will workequally well for this. This process is also useful inthat it will blacken stainless steel.
Another quick blue method is to first cleanthe metal with a solution of potassiumbichromate-sulfuric acid mixture. The solutionconsists of 3 ounces of potassium bichromate (achemical commonly used in photographicdevelopment and available at photo labs), 2ounces of sulfuric acid, and 24 ounces of water.It is then washed with ammonium hydroxide and
102
THE AR-15/M16
rubbed dry. A coat of ammonium polysulfide isnext applied and allowed to dry while beingrubbed briskly with a soft cloth. This is repeateduntil the desired color is reached. The resultingcolor is a deep blue, which will turn almost blackwith repeated applications. The color can bedeepened still more by rubbing with boiledlinseed oil. This results in a finish that isextremely rust-resistant but will not wear as wellas the nitrate or rust blue finishes describedearlier. Both of the finishes described here are,however, quick and cheap.
Both of these methods use sulfuric acid in atleast one mixture. Therefore, rubber gloves andeye protection should be worn when applying.
The ammonium polysulfide mixture is a paleyellow liquid consisting of ammonium sulfidesaturated with sulfur. The ingredients areavailable from chemical supply houses and olderdrug stores. I first used this process more than 50years ago after discovering a description of theprocess in an old chemistry book. This was duringWorld War II, when many chemicals used inbluing solutions were unavailable or in short
supply. I prevailed upon a lovely young lady by thename of Bernice Hoffman, who was in one of ourhigh school chemistry classes, to make me upsome of this, and a couple of days later shehanded over a bottle of each solution. Thisworked well enough that I used it exclusively untilmy supply ran out. By that time commercialsolutions were once more available, so I went tothem instead. I didn’t make up any more until ashort time ago when I got up another batch justto make sure it worked the way I remembered. Itdoes, and if it were not for the rotten egg smellpresent when the bottle is open, I would go backto using it again for certain jobs.
Most of the metal coloring recipes, orformulas, that I have included in my books areold—at least 50 years or more. Some of themwere old 50 years ago. Some of the chemicals arecalled by different names now, and some youngdruggists won’t even know what you are talkingabout if you ask for them. Older druggists andchemists know about them, however, and most,or all, of them are still available—even though itmay require a little effort to locate them.
103
With the component parts finished andcolored to your satisfaction and reassembled, theproject should be ready for test-firing. It might beassumed that, since the gun was assembled andsemi test-fired before heat-treating and finishingand seemed to work the way it was supposed to, itwill still do so. This may or may not be the case.Parts sometimes grow or otherwise change shapewhile being heat-treated. This can also happenwhen certain types of coloring techniques arepracticed. Still others tend to etch the surface ofthe metal, leaving it slightly rough. In many cases,parts that moved freely around pivot pins duringthe first assembly will no longer do so.
When testing the closed-bolt version, makesure that the extractor will still open far enough tosnap over the cartridge rim and hold the case headagainst the bolt face. If it does not, check for burrsor other roughness and make sure the pivot pinstill works freely through the hold in the extractor.
The firing pin should be examined carefully tomake sure that it doesn’t stick in its forwardposition and that it retracts fully when not incontact with the hammer.
Don’t overlook this. One time, earlier on, Icarelessly assembled a bolt similar to the one usedhere, assuming that, since it worked before I bluedit, it still would. When I inserted a magazine withtwo rounds in it, retracted the bolt, and let it slamforward, both rounds fired, even though the safety
was engaged and the trigger wasn’t touched.Subsequent examination revealed that a solidifiedlump of the nitrate salts I used to blue the gun waslodged in the firing pin hole and had jammed thefiring pin in its forward position, effectivelycausing it to become a fixed firing pin. Anothertime I test-fired a 9mm pistol of similar design.This one had been fired numerous times severalmonths before. It had worked perfectly then. Butthis time, when I let the bolt go forward, all fiverounds in the magazine fired. Examination showedthat the firing pin retracted just the way it wassupposed to and moved back and forth withoutbinding. When the action was cycled slowly byhand, the hammer remained cocked until thetrigger was pulled. It was eventually discoveredthat the sear pivot pin had rusted, causing justenough drag that although the hammer remainedcocked during the forward movement of the bolt,the jarring effect when the bolt slammed fullyclosed caused the hammer to slip off of thepartially engaged sear. This, in effect, resulted in aclosed-bolt, hammer-fired machine gun. Theseexperiences prove three things: first, that I am notperfect; second, that I should have loaded only oneround for test-firing, as I have advocated here; andthird, that nothing should be taken for granted.Always check these things carefully, and whentest-firing, keep the muzzle pointed downrange.
The first test-firing should be done by inserting
(FIRING ANDADJUSTING
104
THE AR-15/M16
a magazine containing a single round, retractingthe bolt, and allowing it to slam forwardunimpeded, as it would in the firing cycle. Itshould push the round out of the magazine andinto the chamber. Before firing is attempted,retract the bolt slightly to ascertain whether theextractor snapped in place over the cartridge rim.If it didn’t, the spring is too stiff or there ismechanical interference, which should becorrected before test-firing proceeds further. Thiswill usually be done by substituting a weakerextractor spring or locating and removing metalfrom the place where interference or contactoccurs. Usually, coating the exposed extractorsurfaces with lipstick or the like and working thebolt a couple of times with a cartridge in thechamber will show where the problem is.
If the bolt closes completely and the extractorworks the way it is supposed to, the gun should beheld so that it points away from you and any closespectators and the round fired. Ideally, the roundwill fire and the bolt will travel to the rear, ejectingthe empty case in the process, and move again tothe closed position.
Failure to fire can be caused by several things.Perhaps the firing pin is too short. This can bechecked by removing the barrel, and, with thehammer forward against the base of the firing pin,measuring from the face of the receiver to the boltface. Another measurement is taken from the faceof the receiver to the protruding firing pin tip. Thislast measurement is subtracted from the first, andthe result will be the amount of firing pinprotrusion, which must be at least .055 inch. If itis not, the shoulder in the firing pin hole, whichlimits its forward travel, must be deepened acorresponding amount.
Failure to fire can be the result of the chamberbeing cut too deep, also known as excessive headspace. (Go back and read what I said about thisearlier.) This condition can be corrected by cuttingback the front edge of the receiver an appropriateamount. This will allow the barrel to move fartherback into the receiver. The same result can beachieved by cutting back the front face of the boltbody—not the small, counterbored bolt-noseportion, but the larger outer body. Either of these
actions will close the gap between the barrel andchamber and the bolt face, which, when done inthe required amount, will correct the excessivehead space.
As it turns out, though, the round does fire,due mainly to your precision workmanship andattention to detail. So we can now load two roundsand try it again. If both fire and eject, five roundsshould be loaded and fired, followed by severalloadings of not more than ten. Full magazineloadings should be postponed until a hundredrounds or more have been fired, which will tend toloosen up the action and smooth out any roughspots or burrs still present. A fully loaded magazineincreases friction against the reciprocating boltand may very well slow it to a point where itdoesn’t open completely. Thus, the break-in periodto loosen it up.
It may very well be that even after a break-inperiod the action doesn’t open completely whenthe magazine is fully, or almost fully, loaded. Thisis evidenced by failure to eject empty cases and/orfailure of the bolt to open far enough to pick upthe next round from the magazine. This canusually be cured by shortening the recoil springs,which should be done slowly, a coil or two at atime, test-firing each time, until the bolt openscompletely. This too has its drawbacks, in thatenough spring pressure must remain to close thebolt completely. So don’t overdo it.
The open-bolt version is tested and adjusted inessentially the same way, except, of course, thatinadequate firing-pin protrusion can be ruled outas a cause of failure to fire. This time, the boltshould remain open when it reaches the end of itsrearward travel while in the semiautomatic mode.Its failure to do so can be caused by an overly stiffrecoil spring. This is corrected the same way aswas done with the closed bolt. Another cause ofthis can be that the sear face is angled forward,causing the bolt to cam it down and out ofengagement. This surface, as well as the surface ofthe bolt it engages, must be square and flat.
As described earlier, full automatic fire iscaused by simply pulling the trigger farther to therear, which cams the sear out of engagement,rendering the disconnector inoperative.
105
I have mentioned several times before that anyand all versions of this project would probably beconsidered illegal if built after the assault weaponslaw went into effect in 1994. My prototype gun islegal, since it was built before that date. At leastthe closed-bolt version is. I no longer have anopen-bolt version or a pistol version. That theopen-bolt version was successful can bedemonstrated by the fact that BATF agents seizedthe one I had completed to illustrate this book andcharged me in federal court with illegal machinegun manufacture. Fortunately, I was aware of whatthey had in mind from the beginning and I wasacquitted. But they proved that the gun worked.
Since the muzzle of that particular versionisn’t threaded, if the bayonet lug were removedand the magazine cut off to where it would onlyhold 10 rounds, it may very well be that it wouldbe legal. I wouldn’t count on it, though. If federal
agents catch you with any version of this gun andthey think they can convince a jury that it wasbuilt after the cut-off date, they will very likelyfile a charge against you—or, at least, confiscateyour weapon.
I think (note that I say, I think) that if onlythe upper assembly is built and attached to anexisting lower, this would result in a legal weapon.But don’t depend on it. This too could change atany time.
If the time should come, however, when yousimply must have a weapon such as this forsurvival or defense, then it isn’t going to makemuch difference what is legal and what isn’t. Untilthat time comes, however, I suggest that yousimply practice making parts. And maybe storesome away to use in the future—although eventhat may be considered illegal by some. Do so atyour own risk.
(CONCLUSION
This page intentionally left blank.
