Firearms IdentificationBackground Information

BallisticsMrs. Ashley

Name _______________________________________________

Firearms identification can be defined as: The identification of fired bullets, cartridge cases or other ammunition components as having been fired from a specific firearm.

Firearms identification is actually a form of Toolmark Identification where the firearm, because it is made of a material harder than the ammunition components, acts as a tool to leave impressed or striated marks on the various ammunition components that come into contact with the firearm.

Firearms evidence submitted to a lab's Firearms Section will typically include a firearm, fired bullets, spent cartridge cases, spent shot shells, shot, shot shell wadding, live ammunition, and clothing.

Important vocabulary for this unit:

1. barrel: the long metal tube that guides a projectile out of a firearm.

2. breech: the end of the barrel attached to the firing mechanism of a firearm where the cartridge is loaded and unloaded. This is where breech marks are made on the bullet

3. bullet: the projectile that is released when a firearm is discharged

4. caliber: a measure of the inside diameter of a firearm barrel

5. cartridge: a case that holds a bullet, primer powder, and gunpowder

6. fully automatic: a firearm with a clip-fed mechanism that fires repeatedly as long as the trigger is pressed

7. gunshot residue (GSR): the tiny particles expelled from a firearm when it is fired

8. impressed action marks. Impressed marks are created on cartridge cases when it impacts the tool (again, the firearm) with adequate velocity or pressure to leave an impressed or indented mark.

9. lands and grooves: the ridges (lands) and depressions (grooves) found on the inside of a firearm's barrel that are created when the firearm is manufactured

10. muzzle: the end of the barrel from which the projectile exits a firearm

11. pistol: a hand held firearm

12. revolver: a pistol with a revolving cylinder

13. rifle: a firearm that has a long barrel; a long gun.

14. riffling: the spiral pattern of land and grooves in the barrel of a firearm

15. semiautomatic: a pistol with a clip-fed mechanism that fires one shot per pull of the trigger; the empty cartridge ejects and the next cartridge advances automatically

16. shell casing: the metal usually brass housing for the gunpowder of a firearm

17. striated action marks. These "scratches" are produced when the cartridge case moves laterally against the tool (inner surface of the firearm) producing a scrape or striated mark.

18. trajectory: the path of flight of a projectile.

19. magnum: refers to the use of higher energy gunpowder or more gunpowder

20. rim fire or center fire: refers to where on the rear of the cartridge the firing pin strikes the cartridge casing , either along is rim or in the center. Smaller caliber cartridges tend to be rim fire, while larger cartridges tend to be center fire.

Forensic Examination of Firearms:

In addition to comparing ammunition components to firearms, firearm examiners conduct other examinations that usually include the following:

Testing firearms to determine if they function properly.Examine clothing and other items for gunshot residues and/or shot patterns in an attempt

to determine a muzzle-to-garment distance.Determine caliber and manufacturer of ammunition components. Including the

examination of various shotshell components.Determine the manufacturer or manufacturers of firearms that may have fired a particular

bullet or cartridge case.

Studies have shown that no two firearms, even those of the same make and model, will produce the same unique marks on fired bullets and cartridge cases. Manufacturing processes, use, and abuse leave surface characteristics within the firearm that cannot be exactly reproduced in other firearms.

Firearms do not normally change much over time. This allows for firearms recovered months or even years after a shooting to be identified as having fired a specific bullet or cartridge case. Tests have been conducted that found that even after firing several hundred rounds through a firearm the last bullet fired could still be identified to the first.

It should be noted that not all firearms leave consistent reproducible marks. But overall around eighty percent of the firearms that are examined produce what is sometimes called a "mechanical fingerprint" on the bullets and cartridge cases that pass through them.

All cases that involve firearms identification start with preliminary examinations of the evidence for similar class characteristics. Class characteristics can be defined as: Intentional or design characteristics that would be common to a particular group or family of items.

The class characteristics of firearms that relate to the bullets fired from them includes the caliber of the firearm and the rifling pattern contained in the barrel of the firearm.

Cartridges and Cartridge cases on the other hand are examined for class similarities in what are called breech marks, firing pin impressions, extractor marks, ejector marks and others.

If dissimilarities in class characteristics are found or if a general lack of good class characteristics are present no further comparisons may be necessary.

Bullets collected for comparison to a specific firearm are examined first to see if they are of a caliber that could have been fired from the submitted firearm. They are then examined to determine if the pattern of rifling impressions found on the bullet match the pattern of rifling contained in the barrel of the questioned firearm. If these class characteristics agree the next step is to try to make a positive match between the individual characteristics that may have transferred to the bullet from the barrel.

Located within the rifling impressions on a bullet can be microscopic striations or scratches like those seen on the bullet below. They sort of look like a bar code.

Imperfections in the surface of the interior of the barrel leave striations on the projectiles. Striations have the potential to be consistently reproduced in a unique pattern on every bullet that passes down the barrel of a firearm. The key word in the previous sentence is unique.

Firearm examiners will attempt to find this unique pattern by following the procedures outlined below.

Examinations conducted

Firearm and Bullet Comparison

A submitted firearm will be fired several times using a water tank like the one on the left to obtain standards from the firearm. Lids on the tank are closed and locked and the muzzle of the firearm is placed in the open tube at the end of the tank and fired. Friction from passing through the water slows the bullets down and they end up on the bottom of the tank about halfway down its length. The tank is approximately 3 feet wide, 10 feet long and 3 feet high.

Fired standards, like those to the right, are examined first to determine if in fact the barrel is producing striated marks in a unique and consistent pattern. Once a consistently reoccurring pattern to the marks is identified on standards, the standards are compared to the evidence bullets to see if the same pattern of marks exists on the evidence. To make these comparisons the firearm examiner will use a comparison macroscope (below right).

Notice that this is called a macroscope and not a microscope. Microscopes typically use objectives that are 100x and above. Magnifications typically used in firearms identification are 5X, 10X, 20X, 30X, and 40X. It is not unusual however to see these lower powered scopes referred to a microscopes

All firearm sections will have a comparison macroscope. The comparison macroscope consists of two macroscopes mounted side by side and connected by an optical bridge. There are two stages on the lower part of the macroscope that the bullets to be compared are mounted on. The bullets are attached to the stages using some type of sticky substance.

. The images below show rifling impressions on a 32 caliber bullet at progressively increasing magnifications.

The stages that the bullets are attached to allow the bullets being examined to be rotated on their axis and moved up, down, to the left, and to the right. The bullets are rotated around to see if any microscopic similarities are present. Most positive identifications are made on striations that occur in land impressions and the best marks are usually near the base of the bullets like those seen below.

Not all bullet identifications are like those seen in the above image. Firearm examiners will examine the entire bullet for striations that agree with the standards. Bullets can have as many as six, eight or even twenty-two different land and groove impressions and each one may have areas of agreement between the striations. Taking an image of striations, like the one seen above will usually not be representative of the actual overall positive identification. It really comes down to the experience of the firearm examiner and what they perceive to be the overall uniqueness of the striations that are present.

One of the biggest problems in making an identification is that few evidence bullets are submitted intact. Most are badly distorted, wiped and/or fragmented. The fragment seen below may not look like much but even small fragments and badly damaged bullets can still retain sufficient marks for an identification to be made.

Until the questioned bullet is examined microscopically by a trained firearm examiner you just don't know if it has marks of comparative value. The comparison image below shows the above bullet fragment (right) compared to a standard (left) fired from the submitted firearm.

Cartridge Case Comparison

Like bullets, cartridge cases can be identified as having been fired by a specific firearm. As soon as cartridges are loaded into a firearm the potential for the transfer of unique tool marks exists. However, the cartridge does not have to be fired for these marks to be transferred. Simply loading a cartridge into a firearm can cause unique identifiable marks that can be later identified.

Cartridge cases like those on the right are mostly made of brass but can also be made of other materials such as steel and plastic. Cartridge cases come in a variety of finishes but all are made of a material that is softer than the materials found in a firearm. Any surface of the cartridge case that meets the inner workings of the firearm may be marked.

Tool marks produced on the cartridge cases will be in two basic forms. As the microscopic striations found on bullets, cartridge cases can pick up striated action marks. These "scratches" are produced when the cartridge case moves laterally against the tool (inner surface of the firearm) producing a scrape or striated mark.

The other form of marks that can be left on a cartridge case are impressed action marks. Impressed marks are created on cartridge cases when it impacts the tool (again, the firearm) with adequate velocity or pressure to leave an impressed or indented mark.

Cartridge cases are compared to fired standards from a firearm using a comparison microscope. Standards are first examined to determine what marks, if any, the firearm is consistently reproducing. Evidence cartridge cases are then directly compared to the standards to see if they too are also similarly marked.

Cartridge case comparison results may be reported as follows:

Exhibit 1 (cartridge case) was identified as having been fired by Exhibit 2 (firearm).

The above conclusion is reached if the action marks present on the questioned cartridge case are determined to be because of the actual firing process. An example of which can be breech marks as seen in the comparison image below.

Exhibit 1 (cartridge case) could neither be identified nor eliminated as having been fired by Exhibit 2 (firearm).

The above conclusion is reached if the cartridge case lacks sufficient action marks to be identified as having been fired by the questioned firearm or the firearm in question fails to produce reproducible individual characteristics on standards. All general class characteristics such as caliber and firing pin shape would have to agree. The image below shows a comparison between two cartridge cases that lack any individual characteristics but have a similar general appearance.

Exhibit 1 (cartridge case) was not fired by Exhibit 2 (firearm).

This conclusion can sometimes be reached when the submitted cartridge case exhibits very good individual characteristics that are very dissimilar to those produced on standards. However, consideration must be given to the possibility that the firearm in question could have changed significantly. If all dissimilarities can be accounted for, a negative conclusion will be reached. The comparison image below shows two cartridge cases that exhibit noticeably different breech marks and firing pin impressions.

Exhibit 1 (cartridge case) was identified as having passed through the action of Exhibit 2 (firearm).

This conclusion can be reached if the cartridge case is found to have action marks that result from simply loading and/or unloading a cartridge case in a firearm. The comparison image below shows striated action marks on the shoulder of cartridges that have been loaded and unloaded in a Chinese AK Type assault rifle.

Impressed action marks, with a few exceptions, are produced when a cartridge case is fired in a firearm. The two most common impressed action marks are firing pin impressions and breech marks. Eejector marks can also be in the form of an impressed action mark.

Firing Pin Impressions

Firing pin impressions are indentations created when the firing pin of a firearm strikes the primer of center fire cartridge case or the rim of a rim fire cartridge case. If the nose of the firing pin has manufacturing imperfections or damage, these potentially unique characteristics can be impressed into the metal of the primer or rim of the cartridge case.

The comparison image below shows the firing pin impressions on two centerfire cartridge cases. As you can see, the firing pin impressions have both circular manufacturing marks and parallel marks from a defect in the nose of the firing pin.

The comparison image below shows firing pin impressions on two rimfire cartridge cases. Imperfections in the surface of the nose of the firing pin consistently produced these impressed marks.

Firing pin impressions also can be found on live cartridges. In some cases, the firing pin may miss the primer of a cartridge or fail to strike the primer of a cartridge with sufficient force for it to discharge. The cartridge may also misfire due to a contaminated or deteriorated primer compound. For whatever reason, the result will be the presence of a firing pin impression on the cartridge case of a live cartridge. This could be significant if the cartridge is say, left at the scene or found at a suspect's house. The comparison image below shows light firing pin impressions on an evidence cartridge case (left) and a test standard from a suspected firearm (right).

Breech Marks

By far the most common impressed action marks on cartridge cases are breech marks. Most fired cartridge cases are identified as having been fired by a specific firearm through the identification of breech marks.

Very high pressures are generated within a firearm when a cartridge is discharged. These pressures force the bullet from the cartridge case and down the barrel at very high velocities. When a firearm is discharged, the shooter will feel the firearm jump rearward. This rearward movement of the firearm is called recoil. Recoil is for the most part caused

by the cartridge case moving rearward as an opposite reaction to the pressures generated to force the bullet down the barrel.

When the head or base of the cartridge case moves rearward, it strikes what is called the breech face of the firearm. The image below shows the breech face of a 12 GAUGE, single-shot shotgun.

The breech face rests against the head of the cartridge case and holds the cartridge case in the chamber of the firearm. When the head of a cartridge case slams against the breech face, the negative impression of any imperfections in the breech face are stamped into either the primer of the cartridge case or the cartridge case itself. The image below shows the primer of a shotshell fired in the above shotgun.

Breech marks come in various forms. Those seen above are called parallel breech marks. Obviously, because the marks are a series of parallel lines.

Another form of breech marks are circular breech marks like those seen in the comparison image below.

Breech marks can also show no obvious pattern. They may have a stippled or mottled appearance as seen below.

Here is an example from the Kentucky Police Department about collecting firearm identification evidence:

Evidence Collection Handbook - FIREARM ID

Firearm identification concerns itself primarily with the comparison of bullets and cartridge cases in an attempt to identify the individual firearm from which they were fired. Other examinations conducted under the discipline of firearms identification include muzzle to target distance tests, functional tests to determine if a firearm functions properly and comparisons of bullets and cartridge cases from unsolved murders.

Note: Ballistics is the study of a projectile in motion and is often confused with firearms identification.

Value.

The value of firearm identification is that it allows the investigator, with the aid of the firearms examiner, to reconstruct the events of a shooting. With information gathered from the various tests performed by the firearms examiner, details such as what kind of gun was fired, at what distance and angle, and possibly the exact sequence of events can be determined. Even more important, a bullet or cartridge case can be positively associated with a particular firearm to the exclusion of all others, a claim most other areas of forensic science cannot make.

Information Determined.

Firearms.

A firearm can be tested to determine if it functions properly. The safety mechanisms will be checked to see if the firearm will discharge in an unsafe manner. The amount of pressure necessary to discharge the firearm (trigger pull) will also be measured. Test bullets will be fired and held on file at the laboratory for future comparisons.

Bullets.

Marks produced by tools used in the manufacture of a bullet make possible the identification of bullet brand, caliber, and type. Rifling impressions on the surface of a fired bullet enable a firearms examiner to determine the possible manufacture of firearm from which the bullet was fired. A list of possible makes of firearms will be included on the laboratory report.

A bullet may also be examined to determine whether the bullet was fired from a specific firearm by comparing striated marks visible with the aid of a comparison microscope. The condition of the bullet and/or the firearm may prevent a positive conclusion.

Cartridges and Cartridge Cases.

Cartridges and cartridge cases can be marked by a firearm during loading, firing, or extracting in a manner which allows the firearm examiner to make a positive association between the cartridge or cartridge case and firearm. These marks are produced by the firing pin, breechface, extractor, ejector, chamber and magazines, depending on the type of firearm. Firing pin and breechface markings can positively identify a cartridge case as having been "fired" in a particular firearm.

Extractor, ejector, and chamber marks can be used to associate a cartridge or cartridge case to a particular firearm.

Shot, Wadding.

Recovered shot material normally from a shotshell can be identified as size of lead, steel, copper, nickel or bismuth shot. Wadding material can be examined to determine type of wad, gauge and manufacture.

Shot Patterns.

The distance from which a firearm was fired can be determined by comparing the pattern made by the pellets to test patterns made at various distances by the suspect firearm using ammunition similar to that found in the weapon or at the scene.

Gunpowder Patterns.

The distance from the end of a firearm (muzzle) to a shooting victim or an object can be determined by examining the area around any bullet entrance holes found in the victim's clothing for the presence of a pattern of gunshot muzzle residues. Gunshot residues are projected out of the muzzle of a firearm, at a high velocity and may embed, pass through, or adhere themselves around the bullet hole. By comparing the patterns found on evidence to test patterns produced by the suspected firearm using ammunition similar to that found in the weapon or at the scene, an approximate firing distance (muzzle to garment) can be established.

The absence of powder residues may be due to one of the following:

a shot fired beyond the maximum distance that residues would be deposited by that firearm.

excessive bleeding may wash away any gunshot muzzle residue originally present. there may have been an intervening object such as a pillow, etc., between the gun and the

victim's clothing. in handling the garment, residues may have been dislodged. in the case of a contact shot, the powder residues may have been projected into the

wound, whereby physical characteristics will be indicative of the range of fire.

Open Case File and the Drug Fire System.

Bullets and cartridge cases recovered in unsolved murder cases are retained in each firearms unit of the Forensic Lab. Firearms which are recovered and thought to have some relationship to a particular "open case" can be routinely submitted for comparison. Contact the firearms examiner in your area prior to submitting firearms which are to be compared to the open case file Drug Fire System or the open case file.

Collection.

Firearms evidence carried or sent to the laboratory should be properly recorded, diagrammed (crime scene sketch), marked and packaged. Use the following steps as a guide when submitting firearms evidence.

Firearms.

Do not bring a loaded weapon to the Forensic Lab. Always unload the firearm before submitting it to the laboratory. If the firearm is a revolver, indicate the position of the cylinder as well as the chamber from which each cartridge or cartridge case was unloaded. This can be done by etching the cylinder on each side of the top strap (that part of the frame directly above the cylinder) and

numbering each cartridge or cartridge case as it is removed. A diagram indicating cartridge/cartridge case positions should be made and submitted with the firearm.

Download a Cylinder Contents Worksheet here. (Adobe Acrobat Reader Required)

An example of the diagram to be made by officer recovering revolver can be seen below:

Mark all cartridges and cases with initials, date and numbers to correspond with the numbered chambers in the diagram. The same procedure should be followed with ammunition recovered from autoloading firearms, indicating which cartridge was recovered from the chamber and the position of each cartridge in the magazine. Attach an evidence tag to the trigger guard of each firearm and mark with appropriate information. If mailing the firearm, package it in a rigid container. FEDERAL LAW PROHIBITS MAILING OF LIVE AMMUNITION

Bullets.

A bullet or bullet fragment may be classified as projectiles or components from a live cartridge. Wrap each one in clean tissue paper or cotton and place in a rigid container. Mark on the container the source of each. It is not absolute that you mark an evidence bullet. Putting your marks on a container will suffice. When marking bullets, DO NOT disturb the sides or cylindrical portion of the bullet. Mark bullets on the nose or base.

Cartridges and Cartridge Cases.

Cartridges are live rounds of ammunition which contain components to include a bullet , primer, powder, and cartridge casing. A cartridge casing is a component of a live cartridge or live round of ammunition. Wrap each cartridge or cartridge casing individually in clean tissue paper or cotton and place in a container. Mark on the container the source of each. When marking cartridges or cartridge cases, DO NOT mark near the rim, head, or primer. Mark cartridges and cartridge cases near the mouth of the casing. (Note: All live rounds of ammunition recovered at a crime scene should be submitted to the laboratory when applicable.

Shot, Wadding.

Recover as much of the shot material as possible. Do not damage the shot when recovering. Recover all wading. Place in a container. Package pellets and wads from different locations in separate containers. Mark on the container the source of each. DO NOT mark pellets or wads.

Shot Patterns.

If a shot pattern is present at the crime scene, on an object, or on a victim which cannot be submitted to the laboratory such as a wall, car, house, etc., a scaled photograph should be taken first. Then shot material should be removed from the item.

Powder Patterns.

If articles of clothing are to be forwarded to the laboratory to determine the presence of gunpowder residue, make sure it has been air dried before packaging. Then place cardboard or paper inside the garment (see diagram A below) and button the garment. Cover in a manner that will put the bullet hole and the surrounding area between the two pieces of cardboard or paper and staple or slip into a fixed position (B). A piece of cardboard or paper should also be placed in back of the shirt. If the item must be folded, fold only twice as shown by broken lines (C). Fold arms over outside of cardboard or paper; one in front and one in back. Package each article of clothing to be submitted to the laboratory individually in a paper sack. DO NOT use plastic bags.

Shipment.

Live ammunition cannot be sent by U.S. mail. Firearms, and then only if unloaded, i.e., with no live ammunition, can be mailed only U.S. registered mail. Live ammunition should be hand-carried to laboratory. In special circumstances, UPS may be the only legal way to ship ammunition when other means are not possible. You must have package marked "Ordnance." If any clothing is to be sent that is stained with blood or other body fluids, the package must be marked "BIOHAZARD" or possess a biohazard label. Bloody clothing must be dried prior to shipment.