modellers reference 75mm pak mountain gun

46
,--i';"t.lTi; ,4t-_\ ffi-*--*): 75 M/M MOUNTAIN 'W GUN NATIONAL FORGE & ORDNANCE CO. IRVINE, WARREN COUNTY, PENNA., U. S. A. 'A F]?"h "T,?r$ffi,* ; ru^d '+l(' ' e .- /l ^L\ n'\9r* - O"W tt\ *

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Page 1: Modellers reference 75mm pak mountain gun

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75 M/M

MOUNTAIN

'WGUN

NATIONAL FORGE & ORDNANCE CO.IRVINE, WARREN COUNTY, PENNA., U. S. A.

'AF]?"h

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Page 2: Modellers reference 75mm pak mountain gun
Page 3: Modellers reference 75mm pak mountain gun

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75 M/M MOUNTAIN GUN

FIRING POSITION

7 5 M/rU MOUNTAIN GUN

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Page 4: Modellers reference 75mm pak mountain gun

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75 M/M MOUNTAIN GUN

TRAVELING POSITION ON WHEEIJS

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Page 5: Modellers reference 75mm pak mountain gun

SPECIFICATIONSDiameter of Bore

Length of Barrel, Including Chamber

Length of Barrel, in Calibers

Length of Rifling

Number of Grooves

Width of Grooves .

Depth of Grooves .

Width of Lands

Rifling

Muzzle Velocity

Volume of Powder Chamber

Density of Loading (approx.)

Travel of Projectile

Weight of Projectile

Weight of Charge (approx.)

Powder Pressure (approx.)

Maximum Range

Range of Elevating Mechanism .

Traverse Right

Traverse Left

Weight of Cartridge Case

Length of Cartridge Case

Center Line of Barrel to Ground Line

Wheels

2.952"... 75 M/M62.29"...1592M/M

2r.l

52.90"...1344M/M

28

.1966"...4.739M/M

.030". .. .762M/M

.1444...3.672M/M

IJniform, Right-hand Twist, One Turn inCalibers

1440 Feet per Second

438.9 Meters per Second

45 Cubic Inches . . .737.4 C.C.

.630

52.9" ...L344.M/M14.5 lbs. . . .6.577 Kc15.3 oz. . . .433.7 Grams

23,000 lbs. per Square Inch

1617 KG per Square CM

10,690 Yards . . .9,775 Meters

-5 Degrees. . . 50 Degrees

15 Degrees

15 Degrees

2lbs.....907KG ,8.75"...222.25M/M

40" . .. 1016 M/M32" Diameter, 4tt Tire Steel Wheel, Solid

Rubber Tire or 6" -20 Pneumatic Tires

25

-

Center to Center of Wheels

Maximum Length of Recoil

Ground 48" . . . L2L9.2 M/M. 33.78,, . . .858 M/M

on

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Pcrge 4 7 5 rvrlM MoUNTAIN GUN

Page 6: Modellers reference 75mm pak mountain gun

i Loads

SPE CIFICATIONS - (co,,tinued )

I W.iUht of Gun in Firing position 1825 lbs. . . . 827.8 KG

, Gun Barrel One-piece Forging, with Screwed-on BreechI' Breech Mechanism Semi-automatic, with Vertical Sliding Wedge

BlockII Cradle With Tobin Bronze Slides to Support Recoil_

I ing parts of Gun

I Spring-Recuperators To Balance the Tipping Parts of Gun at Al1Times

IJ Recoil Brake Hydro_pneumatic with Hydro Counter _Recoil Buffer

) f,ower Carriage Welded Construction with Ball Bearings

Upper Carriage Welded Construction with Ball Bearings

I sptit Trails Length of Trails from Center of Wheels toTrail Spades: 94.5" ...2400ls,{/M

Maximum Load. . . 255 lbs. . . . 115.7 KGBarrel 225 lbs. . . . 102.05 KGBreech 165 lbs. . . .74.84 KGCradle 255 tbs. . . . 115.20 KGUpper Carriage .- 255 lbs. . . . 115.70 KGLower Carriage

Wheels I7S lbs. . . .79.37 KG for 2 with pneumatic

Trails

Tires

255 lbs. . . . 115.7 KG for 2 with Solid RubberTires

315 lbs. . . . 142.88 KG for 2

Equilibrators 60 lbs. . . . 27.2 for 2

Upper Shield 170 lbs. . . .77.t KG

Lower Shield 60 lbs. . . . 27.2 KGTotal Weight 1825 lbs. with pneumatic Tires . . . g27.8 KG

f'SOS tns. with Solid Rubber Tires . . . g64.1 KG

7 5 M/M M O U N T A I N G U N pcrse5

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Page 7: Modellers reference 75mm pak mountain gun

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METHOD OF ASSEMBI,ING GUNFROM PACK ANIMAIJS

1-Unpack the lower carriage, wheels, and trails.

2 -Unfold trails (Fig. to traii hinge.

Fig. 2

3-Place wheels on axle sleeve with counterbored part of hub next to trail (Fig. 2).

Pcrse6 .7 5 MM MOUNTAIN GUN

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Page 8: Modellers reference 75mm pak mountain gun

Fig. 3

4-secure in place by winged hub nut. Drive nut tight with lead hammer (Fig. 3).

5-Lay wheels with trails attached on thb ground about four feet apart, hub cap down(Fig. a).

6-Set lower carriage arm in axle yoke with detent pin in its recess.

7 5 M/M MOUNTAIN GUN PcrseT

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Page 9: Modellers reference 75mm pak mountain gun

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7-Swing carriageabout detent pin tovertical position andinsert king pin (Fig.5).

Fig. 5

8-Tip lower carriage, wheel, and trails about wheel as a fulcrum until lower carriage ishorizontal.

9 -Stand up remain-ing wheel with trailattached and slipaxle yoke over endof lower carriage(Fig. 6), insert kingpin.

Fig.6

MOUNTAIN

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Page 10: Modellers reference 75mm pak mountain gun

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Fig. 7

11-Close trails to traveling position and lock with detents (Fig. 7).l2-Clean any dirt or foreign matter from polished fitting surfaces of both upper andlower carriages.

13-Set the uppercarriage into thelower carriage (Fig.8), with carriagearms toward trailspades.

Fig.8

G U N Pcrse975 M/M MOUNTAIN

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Page 11: Modellers reference 75mm pak mountain gun

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14-Twist the upper carriage about vertical center line until the lugs on upper carriagepintle sleeve enter their recesses in lower carriage. The carriage will then drop into placeand the foot treadle locking device on the lower carriage will lock the upper carriage tothe lower carriage. CAUTION must be exercised to see that the upper carriage is downfirmly against the shoulder on top of the lower carriage. When the carriages are properlyset together the foot treadle will be up to the position it occupied before upper carriagewas set in place and the lower surface of the traversing gear housing will be flush withthe mating ring on the lower carriage.

l5-Raise the trunnion caps on the upper carriage by pressing in on the trunnion caolocking detents.

16-Add the recoilmeihanism (Fig. 9),including the cradleand trunnion bear-ings by placing thetrunnion bearingsinto the bearingpedestals.

17-Engage elevat-ing gear sector withpinion (Fig. 10).

Fig. 10

18-Close trunnion caps making certain trunnion cap detents are locked.

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Pcrge l0 75 M/M MOUNTAIN GUN

Page 12: Modellers reference 75mm pak mountain gun

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19-Elevate thecradle and recoil as-

sembly to its limit.

Fig. 11

20-Set the counterpoise trunnions in the sockets provided for them on the upper car-riage and tip them back until holes in their upper end lines up with the holes in cradlearms (Fig. 11).

21-Insert lockingpins (Fig. 12).

Fig. 12

22-Depress the recoil mechanism to horizontal. CAUTION: With the counterpoisein place do not open trunnion caps unless gun is at maximum elevation, which removestension from counterpoise springs.

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Page 13: Modellers reference 75mm pak mountain gun

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Fig. 13

23-Place barrel across trails (Fig. 13).

24-Open breech, clean and oil threads on barrel and breech. Remove all oil fromshoulders on barrel and breech housing.

25-Screw breech

Pose 12 .

housing onto barrel

7 5 M/M

Fig. 14

by means of the

MOUN

interrupted tfrleaas (Fig. 1a.)

TAIN GUN

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Page 14: Modellers reference 75mm pak mountain gun

26-Hold barrel from turning and set breech housing securely on barrel by giving it aquick turn. '

27-Pldce lifting bars through lifting eye on breech and through eye near muzzle.

28-Slide barrel andbreech assembly on-to the lugs providedfor it on top of recoilcylinder (Fie. 15).The breech housinglocking lug at ex-treme rear end of re-coil cylinder mustenter mating recessin breech housing.

Fig. 15

29-Insert barrellocking pin (Fig. 16)

through barrel andrecoil cylinder to re-tain barrel in place.

Fig. 16

30-CAUTION: The breech must always be opened when assembling or removingbreech housing from the barrel (Fig. 13). Opening the breech draws the extractorsaway from their recesses in the rear face of the barrel permitting the breech housing tobe unscrewed.

7 5 M/IvI MOUNTAIN GUN. Pase13

Page 15: Modellers reference 75mm pak mountain gun

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31-The lowershield (Fig. 17) isadded by simplydropping the ta-pered bracket endsinto sockets on lowercarriage. The brack-ets may be driveninto the socketswith the lead ham-mer.

Fig. 18

32-With the upper shield in its folded position (Fig. 18), remove the two chained. pinswhich hold the lower and middle shield brackets together. Lift both brackets away fromthe shield and replace pin through hole in end of middle bracket and through lower holein lower "Y" brackets thus forming a triangular shaped brace. The shield is then openedout flat and brought to the gun.

Fig. 17

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Pcrge 14 75 M/Nr MOUNTAIN GUN

Page 16: Modellers reference 75mm pak mountain gun

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33-The barrel andrecoil mechanism isinserted through thelarge opening in thecenter of shield (Fig. 19), the lower bracket is set on the lower shield and slid back untilthe "C" opening in triangular brace fits over the flat-sided pin on upper carriage. Theshield is then tipped back and the top "Y" brace is placed. over the nut and pin at the

top of carriage arms.The nut is securedby a wrench (Fig.20).

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Fig. 19

Fig. 20

75 M/M MOUNTAIN GUN. Pcrsets

Page 17: Modellers reference 75mm pak mountain gun

34-The center slideis then inserted inthe slides providedfor it on the shield(Fig.21), and thehold down tape onmain shield is at-tached to hook onslide.

Fig. 21

Fig.22

35-Place sight mount, with sight attached, on left trunnion extension. It will be heldin place by the rotating lock (Fig. 22), and two clamp screws. These screws must be

tightened if sight remains on gun when firing.

36-Remove sight and sight mount when transporting gun on wheels.

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Pcrse 16. ..7 5 IvIlM MOUNTAIN GUN

Page 18: Modellers reference 75mm pak mountain gun

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37-To dismountthe gun reverse theorder of assembly.To remove uppercarriage press foottreadle (Fig. 23).

Fig.24

GENERAIJ INSTRUCTIONS

38-Two locks are provided to lock gun duringtransport. One under the cradle locks the cradle tothe upper carriage. The other at the rear of thelower carriage locks the upper and lower carriagestogether. These locks must be released before elevat-ing or traversing the gun.

39-Leather boots are provided for each end of bar-rel, for the threaded end of breech housing,(Fig. 24),and for the lower end of the pintle sleeve (Fig. 25).

Fig. 25

M/IvI MOUNTAIN

Fig. 23

75 GUN. PoselT

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Page 19: Modellers reference 75mm pak mountain gun

40-The sight andsight mount are tobe assembled andpacked in woodenboxes provided fortheir protection(Fig. 26).

41-A tool box is

provided which con-

tains all the neces-

sary tools for fieldmaintenance and re-pair. An oil PumP'with necessary fit-tings, also gauge andmetal hose for nitro-gen tank connectionare provided (Fig.27.)

42-A small nitrogen tank is provided

system,

with each gun to replenish nitrogen in recoil

Fig. 26

Ftg.27

Page 18 .7 5 M/M MOUNTAIN GUN

Page 20: Modellers reference 75mm pak mountain gun

45-The nitrogen pressure in the recoil system must be maintained at.400 to 450 pounds'

This should always be checked, before firing gun if gun has been inactive for several days'

The nitrogen filler plug will be found in the muzzle end of the left recoil cylinder' Remove

the filler plug and screw in the nitrogen filling adapter assembly (Fig. 28)' which con-

sists of the filler connectioll, gauge, and shut-off valve. when the adapter is screwed in,

the valve should. be closed to test pressufe. The adapter extension will trip the check

valve in recoil system and the gauge will rFcord pressure in cylinder.

46-If the gauge reading is less than 400 pounds the pressure must be increased by

attaching the nitrogen tank to the gun by means of the flexible metal hose and the filling

adapter (Fig. 30). Open valve on tank and meter the proper amount of nitrogen into

system by opening the adapter valve a very small amount. Shut off valve occasion-

ally to check gauge reading. When gauge reading is 450 pounds shut tank valve and

adapter valve. Disconnect metal hose and remove adapter assembly. Replace filler plug.

47 _lf for any reason it is desired to drain nitrogen from recoil system, the adapter should

be put in place as when checking pressure. The valve can then be opened to drain system:

48-After draining the nitrogen, the oil may be drained by removing oil filler plug and'

holding down check valve with a small steel rod. The oil gauge body may also be re-

moved to drain oil if necessary. This should not be attempted without first removing

nitrogen from the sYstem.

Fig. 30

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Page 20 75 M/M MOUNTAIN GUN

Page 21: Modellers reference 75mm pak mountain gun

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METHOD OF PACKING

75 M/M MOUNTAIN GUN

ON

PACK ANIMALS

UPPER CARRIAGE ON PACK

MOUNTAIN GUN75 M/M Pcrse 21

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Page 22: Modellers reference 75mm pak mountain gun

WHEELS AND TOOL BOX ON PACK

UPPER SHIELD AND HINGED TRAILS ON PACK

Pa9e22...7 5 M/M MOUI\TTAIN GUN

Page 23: Modellers reference 75mm pak mountain gun

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CRADLE AND RECOIL CYLINDER ON PACK

7 5 IvIlM MOUNTAIN GUN. Pose23

LOWER CARRIAGE, LOWER SHIELD AND SHIELD SLIDE ON PACK

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Page 24: Modellers reference 75mm pak mountain gun

BARREL ON PACK

BREECH, RECUPERATORS AND SIGHTING

Po9e24...7 5 M/M MOUEQUIPMENT ON PACK

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Page 25: Modellers reference 75mm pak mountain gun

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SIGHTINGTo veilfy parallelisrn of line of siEht and axis of bore

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TELESCOPE

BOR,E

When it is desired to check the parallel-ism of the line of sight of the panoramictelescope and the bore of the gun the fol-lowing method should be followed:

A target should be made to dimensionsshown in Fig. 31. The background of tar-get should be painted white and the aim-ing points black.

The carriage is placed with the wheelsand trails resting upon solid supports ofwood, stone or concrete, the surfaces ofwhich have been carefully leveled so as tobring the axle axis horizontal. The barrelis carefully leveled and a bore sight iq

placed in the bore. The target, Fig. 31,

is set in line with the barrel at a distanceof 150 to 200 feet from the muzzle and in

Fig. 31

a vertical position perpend,icular to theline of sight and at such a height that thehorizontal prolongation of the center lineof bore intersects point "X" on the target.The verticality of the target may be as-

sured by dropping a plumb line from point"A" which should coincide with line"AB".

The gun is carefully bore sighted ontarget at point "X". The panoramic tele-scope is attached to the sight mount. Themount with telescope attached is placedon the left trunnion extension and heldin place by the rotating lock. The sightmount is carefully cross-leveled by use ofthe knurled knob until the level bubbleis in the center of vial. The elevating

7 5 M/M MOUNTAIN GUN Pcrge 25

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Page 26: Modellers reference 75mm pak mountain gun

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Fig. 32

index should be set at "O" and also theelevating micrometer dial, which is thelower dial toward rear of mount. Theangle of sight index, at top center of sightmount, should be set opposite "3" and itsoperating micrometer dial should be setat "O". With the mount so set the sightlevel bubble should be central with itsvial.

If the level bubble is not central aftermaking the above setting, either or bothmicrometer dials must be turned untilthe bubble is central with the level vialand the indexes as near as possible to "3"and "O". The index scales may be movedfor adjustment by unscrewing their re-taining screws and setting them oppositetheir corresponding indexes. After level-ing the mount, and registering the index

pointers with their corresponding scalesetting, the three screws in the end of themicrometer dials are loosened and thedials turned until "O" on the dial scale isopposite the coresponding index on thesight mount body.

The screws are then tightened to lockdial to its worm shaft. When properly ad-justed the "O" on both micrometer dials,and the "O" on the elevating scale shouldbe opposite their index arrows and the"3" on the angle of sight scale should beopposite its index arrow with both levelbubbles in the center of level vials.

With the sight mount level bubbles setcentral with their vials, set all dials andindexes on the panoramic telescope at"O". If the sight is properly set the lineof sight through the telescope will pierce

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Pcrge 26 7 5 M/M MOUNTATN GUN

Page 27: Modellers reference 75mm pak mountain gun

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the target at the point "Y". If the lineof sight through the telescope does notterminate at point "Y" the telescope mustbe adjusted.

If the line of sight is at the correctheight but off to either side of the verticalline through "Y", the correction shouldbe made in the telescope. Set the cross

hairs of the telescope on the target byrotating the lower micrometer dial. Loosenthe three screws in the dial retaining discand set dial "O" to coincide with its indi-cator on the sight body. If necessary theindex plate, below the lower circular in-dex, may also be adjusted by looseningthe fwo index retaining screws. It shouldbe noted that the upper horizontal mi-crometer dial should also be set at "O"and the index opposite "O" on the upper

circular scale when making adjustments.If the line of sight of the telescope is

correct horizontally, but the cross hairsare above or below the aiming point "Y",the telescope should be so adjusted byuse of the rotating head micrometer dial,which is the vertical dial at top of tele-scope, until the line of sight through tele-scope pierces point "Y". The three screwson top of the micrometer dial may beloosened and the dial set with its "O"opposite its mating indicator. Tightenscrews and check line of sight to verifysetting. The scale on the peep sight armshows elevation in hundreds of mils. The"O" on this scale and the "O" on the dialshould be set opposite, their mating in-dexes with the line of sight through tele-scope piercing point "Y" on target.

Fig. 33

NIOUNTAIN75 M/IvI GUN Pase 27

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Page 28: Modellers reference 75mm pak mountain gun

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Page 29: Modellers reference 75mm pak mountain gun

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FIRING MECHANISM

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Drawing O.A.-110 . . . Firing Mechanism

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The firing mechanism (O.A.-110) is ofthe continuous pull type-located in anaxial opening in the breech block. To dis-assemble the firing mechanism withdrawlanyard pin from trigger shaft and removelanyard. With a screw driver press triggershaft retaining detent, (O.A.-108-3 Draw-ing O.A.-115), out of engagement withtrigger shaft and withdraw shaft. Thefiring mechanism housing (O.A.-107-1) is

retained in its opening in the breech blockby three lugs.

Turn the case 60 degrees either side ofassembled position and it may be with-drawn from the breech block. Pry thetrigger yoke O.A.-107-4, out of the firingmechanism housing with a screw driver.Insert trigger shaft to engage sear O.A.-107-6. Press the front end of sear out of

engagement with striker, O.A.-107-3, in-sert a screw driver at the rear of the sleeve

O.A.-107-5 and pry the sleeve and strikerforward until they can be grasped by thefingers and pulled from the case. Removetrigger shaft, and withdraw sear and searspring.

To remove the firing spring, (O.A.-108-6) from striker, hold front end ofstriker in one hand and press the rear ofsleeve against any convenient object tocompress firing spring. Press rear end ofstriker down to unhook it from sleeve andallow sleeve and spring to recede fromstriker. Remove the firing pin cotter andunscrew firing pin.

To assemble mechanism proceed in re-verse order.

7 5 M/M MOUNTAIN GUN. Poge29

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Page 30: Modellers reference 75mm pak mountain gun

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Page 31: Modellers reference 75mm pak mountain gun

BREECH MECHANISMThe breech mechanism, (O.A.-115)' is

of the vertical sliding wedge type, semi-automatic.

To open the breech pull the operatinghandle, (O.A.-112-1), on right side ofbreech housing to the rear until the ex-

tractors, (O.A.-113-4 and 5) lock thebreech block open (down), the handleshould then be returned to its originalposition and locked by the handle latch,(O.A.-114-5). When a round of ammuni-tion is inserted the cartridge case headtrips the extractors, allowing the breechblock to return to its closed position underaction of breech closing spring, (O.A'-1 14-6).

To remove breech block from the breechhousing remove the breech closing springcap O.A.-114-7 and unscrew spring ad-justing nut to relieve spring tension. With-draw operating crank pin O.A.-111-2 andclosing spring with attached parts. Re-

move lanyard pin O.A.-108-1 and with-draw lanyard. Pull cotter pin from end

of locking plate key O.A.-112-5 and driveout key, slide locking plate O.A.-1L2-4 tothe rear and remove it from bottom ofbreech housing (O.A.-105). Rotate handleto rear to unlock it from its latch. Moveoperating crank O.A.-111-1 to rear to re-

move it from its bearings. A slight rota-tion of handle and movement to the rear

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of the crank will allow the rollers on innercrank arm to be removed from the "T"slot in bottom of the breech block. Re-move the crank, and the block may thenbe pushed out of the breech housing fromthe top. The extractors can then beremoved from their slots.

The firing mechanism may be with-drawn either before or after removing theblock from breech housing. Method ofremoving firing mechanism from block isdescribed under "Firing Mechanism".

The operating handle latch may be dis-rnounted from the side of breech housingby removing the cotter pin at the lowerend of key O.A.-114-2 and driving out thekey. Drive the latch assembly to the rearto release it from its dovetail. The plungerO.A.-114-5 and spring O.A.-114-3 areretained by the headed pin O.A.-114-4which fits into the flat recess on the sideof the plunger. Press the top of plungeragainst any convenient object to compressthe spring and with a small screw driveror pin against the outer end of the retain-ing pin, it may be pushed out of the hous-ing. The spring and plunger may thenbe removed, by gradually releasing thepressure on the spring. They can then beremoved from the housing.

To assemble proceed in reverse order'

75 M/ru MoUNTAIN G U N. Pcrse3l

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Page 32: Modellers reference 75mm pak mountain gun

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Page 33: Modellers reference 75mm pak mountain gun

COUNTERPOISETo disassemble counterpoise assembly

(O.A.-149-f), place it in a lathe betweenjaw chuck and tail stock centers andguided by the two steady rests as shownon O.A.-250.

Steady rest No. 1 is lightly clamped tothe outer sleeve of counterpoise and se,curely clamped to lathe bed. The steadyrest No. 2 is lightly clamped to inner sleeveof counterpoise and secured to the lathebed loosely enough to slide freely on thebed as is the tail stock.

The counterpoise spring with the count-erpoise extended as shown is under a pres-sure of about 350 lbs. and therefore to

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prevent injury to the personnel, cautionmust be exercised when assembling anddisassembling this unit. IJnscrew thecounterpoise locking nut and allow innerstreeve, steady rest No. 2 and the tail stockto slide to the right, using the tail stocktraversing crank to control the operation.As the inner sleeve is withdrawn from theouter sleeve, the spring will become ex-posed and should be held from deflectingto either side by hand. At the pointwhere the spring may tend to deflect itsload has, of course, been greatly reduced.

To assemble the counterpoise proceedin reverse order.

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7 5 IvIlM VIOUNTAIN G U N. .Pose33

Page 34: Modellers reference 75mm pak mountain gun

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Page 35: Modellers reference 75mm pak mountain gun

ELEVATING MECHANISMThe elevating mechanism is located on

the left side of gun, secured to upper car-riage by four cap screws. The eccentrichousing which supports the elevatingpinion is clamped at its inner end by fourcap screws. By removing these eight capscrews the assembly may be removedfrom the carriage.

The assembly is shown on O.A.-143 andconsists of a hand wheel, with overruriningclutch, a pair of bevel reduction gears, aself-locking' worm and worm gear andelevating pinion, housed in an aluminumcase and equipped with ball bearings. Thehand wheel may be locked to the shaft bypressing in on the locking jaw at the hubcenter.

To adjust the bevel gears, remove theoil filler plug at top of housing. IJnscrewthe locking screws which lock sleeveO.A.-140-1 and retainer O.A.-139-3 inplace. If only a slight adjustment is nec-essary it may be made by retainer O.A.-139-3. If the back edges of the teeth arenot flush as observed by looking throughthe oil filler hole, then the sleeve O.A.-140-1 must be turned until they are, andat the same time maintaining the properbacklash, which should be just enough toallow bevel gears to turn freely withoutany perceptible looseness.

The worm wheel may be adjusted tothe worm by rotating the eccentric sleeveO.A.-141-1 and locking it in place withlock nut O.A.-141-3.

If it is desired to remove the parts fromthe housing, the following method shouldbe employed. IJnscrew sleeve O.A.-140-lfrom the casing which will draw the worm(O.A.-139-5), bearings and bevel pinion

(O.A.-139-2) to the rear far enough to belifted out of housing by hand. The handwheel with its shaft, bevel gear O.A.-139-1, and bearings may be removed asa unit by removing the locking screw andunscrewing retainer (O.A.-139-3) whichwill draw the assembly out of the housing.

The worm wheel, eccentric sleeve, ele-vating shaft, with pinion, and bearingsmay be removed as a unit from the hous-ing, by removing cover, 0.4.-140-6 andunscrewing the sleeve locking nut, O.A.-141-3 and loosening the two lower clampscrews in the eccentric sleeve clamp, O.A.-142. When removing the cover, O.A.-140-6, a pail should be at hand to catchthe oil contained in the housing. Theseparts run in a bath of oil and when as-sembling, the oil should be replaced. Theworm wheel may be pulled from the shaftafter removing nut, O.A.-140-3. The bear-ing adjacent to the worm wheel is retainedby ring, O.A.-141-2. The shaft and pinionwith the two pinion bearings may beshoved out of the eccentric sleeve fromthe worm gear end.

To assemble the mechanism reverse theprocedure outlined above; adjust the wormwheel to the worm and adjust the bevelgears as previously described. Lock theparts in place and filI housing with lightgear oil to the height of the bottom of thehand wheel shaft. This lubricates all gearsand bearings in the case. The two largebearings on either side of elevating pinionare packed with lubricant and require nooiling.

One turn of hand wheel elevates gun1.33 degrees.

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7 5 M/M MOUNTAIN GUN . Poge 35

Page 36: Modellers reference 75mm pak mountain gun

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Page 37: Modellers reference 75mm pak mountain gun

TRAVERSING MECHANISMThe traversing mechanism, (O.A.-148),

is secured to the rear face of the uppercarriage gear housing by ten cap screwsand two dowel pins. It consists of a wormmounted on self-lubricated ball bearings,inclosed in an aluminum housing. A handwheel at the outer end is provided withan overrunning clutch and a locking mech-anism to lock the hand wheel to the shaftif so desired. The worm meshes with asector on the pintle sleeve which in turnis keyed to the lower carriage. One turnof the hand wheel traverses gun ll( de-grees. Any axial looseness that may de-velop may be taken up by means of theadjusting sleeve, O.A.-147-2 and the lock-ing nut O.A.-147-3.

To disassemble, remove the assemblyfrom the upper carriage. Remove thefour screws in hand wheel hub and thehub cap, jaw and spring. Drive out the

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tapered pin and remove hand wheel as-sembled to its hub. IJnscrew adjustingsleeve, O.A.-147-2 and lock nut O.A.-147-3. The shaft with the two bearingsat the worm may be driven out of thehousing from the hand wheel end. Thebearing at the hand wheel end of housingmay be removed by unscrewing the ringO.A.-L+7-4 and pushing the bearing outfrom the opposite end of the housing.

To assemble proceed in reverse order.To adjust the worm to the worm wheel

a laminated gasket is provided betweenthe gear case and the traversing gear hous-ing. As wear occurs any backlash betweenthe worm and worm wheel may be re-moved by peeling off a lamination fromthe gasket, and replacing the traversinggear. If backlash still occurs after tight-ening cap screws an additional laminationmay have to be removed.

7 5 M/M MOUNTATN GUN.. Poge37

Page 38: Modellers reference 75mm pak mountain gun

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Page 39: Modellers reference 75mm pak mountain gun

TRAVERSING MECHANISMThe traversing mechanism, (O.A.-148),

is secured to the rear face of the uppercarriage gear housing by ten cap screwsand two dowel pins. It consists of a wormmounted on self-lubricated ball bearings,inclosed in an aluminum housing. A handwheel at the outer end is provided withan overrunning clutch and a locking mech-anism to lock the hand wheel to the shaftif so desired. The worm meshes with asector on the pintle sleeve which in turnis keyed to the lower carriage. One turnof the hand wheel traverses gun ll( de-grees. Any axial looseness that may de-velop may be taken up by means of theadjusting sleeve, O.A.-L47-2 and the lock-ing nut O.A.-147-3.

To disassemble, remove the assemblyfrom the upper carriage. Remove thefour screws in hand wheel hub and thehub cap, jaw and spring. Drive out the

tapered pin and remove hand wheel as-sembled to its hub. IJnscrew adjustingsleeve, O.A.-L47-2 and lock nut O.A.-147-3, The shaft with the two bearingsat the worm may be driven out of thehousing from the hand wheel end. Thebearing at the hand wheel end of housingmay be removed by unscrewing the ringO.A.-L47-4 and pushing the bearing outfrom the opposite end of the housing.

To assemble proceed in reverse order.To adjust the worm to the worm wheel

a laminated gasket is provided betweenthe gear case and the traversing gear hous-ing. As wear occurs any backlash betweenthe worm and worm wheel may be re-moved by peeling off a lamination fromthe gasket, and replacing the traversinggear. If backlash still occurs after tight-ening cap screws an additional laminationmay have to be removed.

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Page 40: Modellers reference 75mm pak mountain gun

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Page 41: Modellers reference 75mm pak mountain gun

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RECOIL MECHANISMDESCRIPTION AND ADJUSTMENT

The recoil mechanism, 0.A.-126 is of the stop O.A.-124-2. The oil then flowsthe hydro-pneumatic type consisting of through the communicating passage intothree cylinders bored in a single forging. the recoil cylinder forcing the recoil pistonThe center cylinder contains the recoil back to the rear of its cylinder, and at thepiston, piston rod and packing glands. same time compressing the air, which dur-An adjustable respirator valve, (O.A.- ing recoil was drawn in through the res-120-4), is located in the center cylinder pirator valve O.A.-120-4. The compres-at the breech end. sion of this air cushions the return of the

The right hand cylinder contains the parts. Varying the amount of leakagefloating piston, oil gauge, (O.A.-122-5), past the valve by means of adjustingand recoil regulator, (O.A.-123-4). screw O.A.-120-5 alters the cushioning

The left cylinder is an air reservoir and effect.is connected by a by-pass to the rear end The length of recoil may be increasedof the floating piston cylinder. The for- by increasing the length of stroke of recoilward end of the left cylinder contains the valve. To increase stroke, loosen followernitrogen filling valve, (O.A.-121-5). O.A.-123-6 and unscrew regulator sleeve,

In recoil the recoil cylinders (O.A.-116) O.A.-123-5 a fraction of a turn. One com-slide to the rear with the barrel, being plete turn will open valve .083". Theguided in grooves in the cradle. The piston normal stroke of this valve is .065. If thisand rod are fastened to the front of the setting does not give 32" of recoil thecradle and do not move. As the gun re- opening must be increased by unscrewingcoils the oil at the front end of the main the sleeve (O.A. 123-5) abott rl of a turnpiston is forced through the passage lead- and again checking length of recoil. Theing into the regulator, opening the recoil maximum length of recoil is 33.78" whichvalve O.A.-124-4 against spring O.A.-123-2 is controlled by the sleeve O.A.-119-2 anduntil end of valve strikes lip on end of spring O.A.-119-1. The sleeve slides overcontrol mechanism housing (O.A.-123-4). the communicating passage between recoilThe oil forces the floating piston along its cylinder and regulator, cutting off the flowcylinder, against nitrogen pressure of 450 of oil. Any additional load is absorbedpounds per square inch. The recoilinC by the buffer spring O.A.-119-1.parts are thus brought to rest by the The counter recoil valve stroke may bethrottling of the oi1 through the recoil adjusted by loosening the follower (O.A.-valve, the resistance offered to the float- 124-3) and screwing the stop (O.A.-L24-2)ing piston by the nitrogen and friction of in by means of a screw driver, to shortenthe parts. valve stroke. To lengthen valve stroke

The gun is returned to battery by the unscrew the stop. Hold stop in place andaid of the compressed nitrogen behind the tighten follower with socket wrench. Onefloating piston, which pushes the piston. turn of stop alters valve stroke .055".back and forces the oil into the regulator The normal valve stroke is .220 inch.and as the balanced recoil valve is closed The tool box contains a set of socketdue to action of its spring, the oil pushes wrenches with which to make these ad-the counter recoil valve O.A.-124-1 open justments.until the end of its stem strikes bottom in The recoil system holds 85 cubic inches

7 5 M/M MOUNTAIN GUN Poge 39

Page 42: Modellers reference 75mm pak mountain gun

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Page 43: Modellers reference 75mm pak mountain gun

of oil (about 114 qtatts)' However' 174

quarts is the maximum amount to be used

when refilling.The cylindrical projection of the front

end. of floating piston nut, O'A'-122-2 acts

as a valve to retard the movement of gun

into battery when oil level in system is

low, thus giving warning to the gunners

in case the oil gauge position has not been

noticed.

minor adjustments should be attempted

in the field. If for any reason the system

does not function properly it should be

disassembled in the ordnance repair shop'

To remove the main Piston rod and

piston assembly from the center cylinder'

lhe respirator O.A.-120-1 should be re-

moved from the breach end of cylinder'

also the copper gasket O'A'-120-7' The

For satisfactory operation enough oil

should be maintained in the system to

keep the oil gauge stem O'A'-122-5 flush

-ittr tt. top of gauge body' Methods of

filling nitrogen and oil are covered under

general instructions.

To Disassemble Recoil SYsfernr

First remove the nitrogen filler plug

O.A.-121-4 and insert the nitrogen filler

adapter, with gauge and shut off valve at-

tached which will be found in tool box'

The small projection on end of adapter

will trip check valve O'A'-121-5 allowing

nitrogen to flow into the atmosphere and

,educe the pressure in the system to thatof the atmosPhere.

CAUTION: No Part of the recoil sYs:

tem should be taken apart without first

removing the nitrogen. No repairs except

7 5 M/M MOUNTA

piston rod with piston assernbly may then

te pushed out from the rrruzzle end' The

stuffing box at m'tzzle end maY then be

unscrewed and removed'IJnscrew the regulator housing O'A'-

123-4 with its parts in place' Remove the

cap O.A.-119-7 in the breech end of the

floating piston cylinder' The floating pis-

ton may then be pushed out of its cylinder

from the rrruzzle end with a brass or

bronze rod.The oil gauge housing O'A'-122-4 with

its contained parts may be unscrewed as

a unit.The nitrogen filling valve may be re-

moved by unscrewing the front cap O'A'-

l2l-2 from the left recoil cylinder'No description is necessary for the com-

pleted disassembly of these units, as this

is self-evident from their construction'

I N G U N. Pose4l

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Drawing O.A.-198-1 . . . Method of Applying Recoil Piston to Recoil Cylinder

Page 44: Modellers reference 75mm pak mountain gun

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Page 45: Modellers reference 75mm pak mountain gun

570FF/N6 6a1 PAC4//|6 FECO/L CYL/IDER

from any foreign matter, and. that cylinderwalls are lubricated with a light film ofrecoil oil.

The recoil piston assembly is first in-serted in the center cylinder bore from thebreech end with the aid of the sleeveO.A.-198-2 which is first placed in the

Drawing O.A.-199-2 . . . Sleeve

breech end counterbore of the center cyl-inder as shown in O.A.-198-1. The pack_ings are lubricated and the piston pushedinto the cylinder until about 4 inches ofthe rod extends through the front end ofcylinder. The stuffing box, packing, glandand nut are then applied to the front endof the cylinder as shown on O.A._199_1.The packing should be oiled before apply_ing and both packings with their followersshould be pushed through the sleeve O.A._199-4 at the same time to prevent airpockets between the packings. Remove

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the sleeve after forcing packings againstthe shoulder in cylinder and follow upwith bushing housing O.A.-119-5. Thisshould not be set up too tightly.

The respirator assembly should next beadded to the breech end of center cylinder.This should be screwed up tightly against

Drawing O.A.-199-3 . . . Sleeve

the copper gasket with aid of the socketwrench and a lead hammer.

Next apply the floating piston to theright cylinder aided by the sleeve O.A._198-4 which is inserted in the counterboreat the breech end as shown on O.A.-19g_3.The piston glands and packing must beoiled before assembling. push the pistontoward the front of the cylind.er with acopper or brass rod until the forward. endof the conical nut is just visible throughthe oil gauge opening. Screw in the regu_lator against the copper gasket and also

DO NOT APPLY CLAND PACK|NCUN'/L PBTON W/TH /B 4CK/NCPROPERLY ANU'TED HA5 SEEN/PPL/ED ]N CYL/ilOER

Drawing O.A.-199-1 . . . Method of Applying piston Rod Stuffing BoxPacking to Recoii Cylinder

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7 5 M/M MOUNTATN GUN . Poge 43

Page 46: Modellers reference 75mm pak mountain gun

the plug (O.A.-119-7) in breech endagainst its copper gasket. Set both uptightly with the socket wrench and leadhammer. Screw in the oil gauge body andits contained parts, the oil filler assembly,and the front cap containing the nitrogenfilling valve. Make certain these are se-

curely tightened against their gaskets.The system is then ready to charge with

oil and nitrogen as previously described.The gun is then read.y to be fired. Any 'minor adjustments to vary the recoil orcounter recoil may then be made as pre-viously described.

IJse special recoil oil furnished with gun.Additional oil may be obtained from theNational Forge & Ordnance Company.

Drawing O.A.-f99-4 . . . Sleeve

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