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.

 

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