Firearm Identification

THE SCIENCE OF FIREARMS

IDENTIFICATION INCLUDES:

• Comparison of bullets and cartridge

casings

As well as:

• Knowledge of all types of weapons

• Restoration of obliterated serial numbers on

weapons

• Detection and characterizations of

gunpowder residue on garments / around

wounds / hands

• Estimation of muzzle-to-target distances

Ballistics is the study of the trajectory

taken by bullets!

•There are literally thousands of types of firearms!

They can be classified as shoulder firearms (rifles

and shotguns) and handguns (pistols, revolvers,

etc)

Revolver

Semi Automatic

Firearms can also be classified

as “smoothbore” (shotguns) or

“rifled” (most other weapons)

•A gun barrel is produced from a solid bar of steel

by drilling. The manufacture of a barrel also requires

the impression of spiral grooves on the inner

surface. This is called “rifling”. The surfaces of the

original bore are called lands. The diameter of a

gun barrel, measured land to opposite land is

called the “caliber” of the weapon. It is measured in

hundredths of an inch or in millimeters.

•The lands and grooves guide the bullet through the

barrel, giving it spin, so that it does not tumble,

thus increasing its speed and force

CALIBER

If this is a land

impression, what

are the other

areas?

Land

Land

Land

Groove

Groove

Groove

Caliber

• Every firearms manufacturer

chooses a rifling process, giving the

weapon class characteristics.

Frequently, a firearms examiner is

given a spent bullet without a

weapon. The caliber, weight, etc.

help determine the weapon. The

FBI maintains a record of class

characteristics known as the GRCF

(Gallery Rifle Centre Fire).

Bullets

Full Metal Jacket vs Hollow Point

• Some bullets are described as full metal jackets (FMJ) and some are described as hollow points (HP).

– A hollow point is designed to stay inside the victim, as to not potentially exit the victim and strike someone else.

– These bullets are often used by police so that other spectators aren’t injured.

– A full metal jacket is designed to pass through the victim.

Bullet Types

•The marks or striations on

the inner surface of the barrel

are randomly irregular and

make each unique. As the

bullet passes through the

barrel, its surface is

impressed with unique rifled

marks of the barrel.

•There are small changes

due to grit, dust, & wear.

•Recovered evidence bullets may become so

distorted on impact as to yield only a small area

with markings.

9mm LUGER caliber G.F.L.

(Fiocchi) FMJ bullets.

38 SPECIAL caliber plain lead bullet.

32 S&W LONG caliber

plain lead bullet.

22 caliber copper-washed and

plain lead bullets.

A comparison microscope is used to

compare striation marks. No rules govern

the points needed for bullet comparison.

A bullet is slightly larger in diameter than the bore diameter of the barrel in which it is designed to be fired. The bore diameter is the distance from one land to the opposite land in a barrel. As a result, a rifled barrel will impress a negative impression of itself on the sides of the bullet like those seen below.

Water tank

Weapons are test fired into a recovery tank

containing water

Pulling the trigger serves

to release the weapon’s

firing pin, causing it to

strike the primer, which

ignites the powder.

The burning gunpowder

generates gases that

expand and propel the

bullet forward, and the

spent cartridge case

back against the breech

block.

The shell therefore also

has unique markings!

Bullet and cartridge case identification

through comparison microscope

Comparison microphotograph of two bullets

Land Impression Striations

380 AUTO caliber FMJ bullets

fired from a EAA Corp. pistol.

9mm LUGER caliber FMJ bullets

fired from a BROWNING pistol.

Groove Impression Striations

38 SPECIAL caliber

lead bullets

fired from a ROHM

revolver.

38 SPECIAL caliber

SJHP bullets

fired from a TAURUS

revolver.

A shotgun shell is diagrammed below:

Gauge: Refers to the

diameter of the barrel on

a shotgun in terms of the

number of lead balls the

size of the bore it would

take to weigh one pound

(10 gauge, 12 gauge,

etc.) ".410 gauge" really

refers to caliber, but is

worded as such to refer

to a shotgun.

Bullets, shot pellets,

and other projectiles

may be recovered

from the crime scene

or from the bodies of

shooting victims. Fired

cartridge cases, fired

shot shells, shot shell

wadding, unfired

ammunition and

components may also

have evidentiary

value.

Mottled

breech marks

Parallel

breech marks

Circular

breech marks

Types of Breech

Marks

Matching breech marks Breech marks do not match

Firing pin impressions

38 SUPER AUTO cartridge

cases fired in a COLT pistol.

Drugfire Computerized Firearms

Comparison System

Gunshot Residue

The deposition of gunshot

residue on evidence such

as clothing varies with the

distance from the muzzle

of the firearm to the target.

Patterns of gunshot

residue can be duplicated

using a questioned firearm

and ammunition

combination fired into test

materials at known

distances. These patterns

serve as a basis for

estimating muzzle-to-

garment distances.

Gunshot residue patterns.

Muzzle Blast of a Shotgun

T-shirt chemically treated for the presence of lead residue.

Heavy deposits of lead found along left shoulder.

Close-up of bullet entrance hole in above shirt.

Lead bullet wipe residues (pink) noted around the hole.

9-inch test standard showing visible particulate residue (lead, burned and

unburned gunpowder) and vaporous lead (pink) residues.

3-inch test standard

showing a very

concentrated

deposit of soot and

vaporous lead

residues.

Griess Test from the 3-inch test

standard. Orange color is a

positive reaction to a presence

of a pattern of nitrite residues.

Soot is seen on the hand of a suicide victim,

giving an indication that he was holding the

weapon when it was fired.

Collection and Preservation of

Firearms Evidence

• Never stick an object into the barrel

• Pick up the gun by the edge of the trigger guard or on the checkered portion of the grip – these areas do not usually retain prints

• Weapons recovered in water must be transported to the lab in the same water to prevent rusting in transit

• Ammunition must never be dug out of a wall or other surface – remove the whole section surrounding the bullet in order to reduce the possibility of adding any stray scratches, etc.