Firearms IdentificationFirearms Identification

Forensic firearms examinationsForensic firearms examinations

identification of a bullet, cartridge case, or identification of a bullet, cartridge case, or other ammunition component as having other ammunition component as having been fired by or in a particular firearm. been fired by or in a particular firearm.

the possibility for such singular the possibility for such singular identification can be attributed to specific identification can be attributed to specific machining processes used in the machining processes used in the manufacture of firearms.manufacture of firearms.

RiflingRiflingHelical grooves (rifling), cut into the bore Helical grooves (rifling), cut into the bore

of a barrel of a firearm during production, of a barrel of a firearm during production, increase the accuracy of that firearmincrease the accuracy of that firearm

Effects:Effects:SpinSpinStabilizedStabilizedMarks on the bullet (lands and grooves)Marks on the bullet (lands and grooves)

A rifled barrel:A rifled barrel:will contain scratches, scrapes, and other will contain scratches, scrapes, and other

minute nicks and flaws minute nicks and flaws exacerbated through the subsequent use and exacerbated through the subsequent use and

discharge of the firearm discharge of the firearm or as a result of natural wearing processes or as a result of natural wearing processes

such as rusting and corrosion such as rusting and corrosion bullet will have unique microscopic bullet will have unique microscopic

markings as a resultmarkings as a result

Firing pin impressions:Firing pin impressions:

During the discharge of a firearm, the firing During the discharge of a firearm, the firing pin strikes the primer of a cartridge, pin strikes the primer of a cartridge, creating microscopic contact marks and creating microscopic contact marks and unique indentations. unique indentations.

Breechface impressions:Breechface impressions:

As the powder within the cartridge begins As the powder within the cartridge begins burning, the cartridge case is propelled burning, the cartridge case is propelled backwards against the breechface with backwards against the breechface with enough force to be impressed with the enough force to be impressed with the characteristic microscopic features of that characteristic microscopic features of that surface.surface.

When no firearm is recovered:When no firearm is recovered:

rifling parameters taken from the recovered rifling parameters taken from the recovered bullets can be used to determine the possible bullets can be used to determine the possible manufacturers of the firearm from which the manufacturers of the firearm from which the bullets were fired. bullets were fired.

General rifling characteristicsGeneral rifling characteristics or or GRCGRC are the are the identified rifling pattern (i.e. 8/right) and the identified rifling pattern (i.e. 8/right) and the diameters of the individual lands and grooves.  diameters of the individual lands and grooves. 

Using these parameters, firearm examiners can Using these parameters, firearm examiners can search through a database of known rifling data.  search through a database of known rifling data. 

A typical GRC search:A typical GRC search:

a 9mm LUGER bullet, fired from a 6/right a 9mm LUGER bullet, fired from a 6/right rifled barrel, with a land width of .055 and rifled barrel, with a land width of .055 and a groove width of .125. a groove width of .125. 

Results of Search:Results of Search:

CARTRIDGE MANUFACTURER TWIST L&G LANDGROO

VE

9MM LUGER AA ARMS INC R 6 .055 .120

9MM LUGER ASTRA R 6 .053 .128

9MM LUGER BERETTA R 6 .055 .130

9MM LUGER HI-POINT FIREARMS R 6 .055 .120

9MM LUGER INTERDYNAMIC R 6 .055 .124

9MM LUGER LLAMA R 6 .054 .120

9MM LUGER MAUSER R 6 .054 .128

9MM LUGER SMITH & WESSON R 6 .056 .122

9MM LUGER STAR R 6 .054 .126

9MM LUGER SWD INC R 6 .055 .120

FBI Database:FBI Database:

The database used by firearm examiners The database used by firearm examiners all over the world is compiled and all over the world is compiled and maintained by the FBI. maintained by the FBI.

The FBI has been recording rifling data The FBI has been recording rifling data from firearms for over 20 years. from firearms for over 20 years.

As new firearms are manufactured, the As new firearms are manufactured, the rifling data is included in the database. rifling data is included in the database.

Case StudyCase Study Many years ago, a double murder occurred in Many years ago, a double murder occurred in

our community. An elderly couple was found our community. An elderly couple was found shot to death in their home by their son. shot to death in their home by their son.

It appeared from the scene that there had been It appeared from the scene that there had been a break-in but the son was immediately a a break-in but the son was immediately a suspect. Investigators had a feeling that the son suspect. Investigators had a feeling that the son may have committed the crime but could not may have committed the crime but could not determine if he had owned or had access to a determine if he had owned or had access to a firearm. firearm.

Bullets from the scene were examined and it Bullets from the scene were examined and it was determined that they were of 38 caliber and was determined that they were of 38 caliber and were fired from an 8/right rifled barrel. were fired from an 8/right rifled barrel.

Case StudyCase Study A list of manufacturers was compiled and given A list of manufacturers was compiled and given

to the investigators. to the investigators. Using this list, the investigators searched a Using this list, the investigators searched a

weekly "Bargain Mart" classified ad publication. weekly "Bargain Mart" classified ad publication. By calling the ads for firearms included on the By calling the ads for firearms included on the list of possibilities, the investigators found one list of possibilities, the investigators found one individual who said he had sold his revolver to individual who said he had sold his revolver to an individual who matched the description of the an individual who matched the description of the son. son.

The son was then picked out of a police line-up The son was then picked out of a police line-up by the individual who had sold him the gun. by the individual who had sold him the gun. When confronted with the evidence the son When confronted with the evidence the son confessed to the killings. confessed to the killings.