Firearms Identification

A discipline mainly concerned with determining whether a bullet or cartridge was fired by a particular weapon.

3 Areas of Interest Internal ballistics What happened when the gun is fired? External ballistics What happened to the bullet and residues outside of the gun? Terminal ballistics Where did the bullet go?

Anatomy of a Bullet Cartridge Case Gun Powder Lead Bullet Primer

#1 The expanding _____ generated by the burning of gunpowder propels the bullet forward through the barrel. A.Liquid water B.Solid primer C.Gases

Breech Extracting Pin Firing Pin Ejector (not shown) Anatomy of a Firearm

When a cartridge is fired, the explosion forces the bullet down the barrel and the shell casing is forced back against the breech. This leaves impressions unique to the individual gun’s breech on the shell casing. Breech

Broach Cutter

Rifling The spiral grooves that are formed in the bore of a firearm barrel. Makes projectile spin when fired.

#2 What is the benefit of using a firearm that is rifled? A.The bullet will be fired with greater accuracy B.The bullet will be fired faster C.The bullet will not be damaged when fired

Shotgun identification Shotguns have smooth barrels with no rifling. Therefore there are no land or groove marks left on the bullet. Identification can still be made by comparison of extractor/ejector markings on shotgun shell.

A B A B B Barrel -A) Land -B) Groove Rifling Impressions on a Bullet -A) Land impression -B) Groove impression

#3 True or False. Since manufacturers typically use a broach cutter that impresses the same number of lands and grooves on a barrel, then all guns made by a company are identical. A.True B.False

A) Land impression B) Groove impression A B

#4 Given the image of the bullet below, what conclusion can be drawn. A.This bullet has not been fired from a weapon B.This bullet was fired from a rifle or handgun. C.This bullet was fired from a shotgun.

Caliber - the diameter of the bore of a rifled firearm. The caliber is usually expressed in hundredths of an inch or millimeters. Example.22 caliber or 9mm. A

#5 Caliber is measured from: A.Land to groove B.Land to land C.Groove to groove

Bullet Comparison Class Characteristics Different gun manufacturers use different rifling techniques. These techniques impart the class characteristics of a bullet. -Brand -Size -Number of lands and grooves -Width of lands and grooves -Depth of lands and grooves -Pitch -Twist

Bullet Comparison Individual Characteristics A cross section of a gun barrel will show small grooves or striations all along the lands and grooves (machine markings) These are created when the barrel is rifled.

Bullet Individual Characteristics A B

#6 Which of the following is not a class characteristic of bullets. A. Number of lands and grooves B. Width of lands and grooves C. Striations D. Pitch E. Brand and size of the bullet

Cartridge Case Class Characteristics Manufacture ( i.e.. Winchester) Shape ( i.e.. rimless, rimmed ) Caliber ( i.e.. 45 ACP, 9mm, 12gauge) Composition ( i.e.. brass, steel, plastic)

Cartridge Case Individual Characteristics -Firing Pin Impressions -Breech Face Marks -Ejector Marks -Extractor Marks Breech Extracting Pin Firing Pin

Examples of Breech Markings

Firing Pin Marks

Firing Pin Mark Breech Marks

Extracting Pin and Ejector Marks The extracting pin and ejector throw the spent shell casing from the chamber of the gun. These leave marks on the shell casing that are unique to those parts on that particular firearm.

#7 Which of the following is not an individual characteristic of cartridge cases. A. Firing pin impressions B. Caliber C. Breech face marks D. Ejector marks

#8 Given the image of the cartridge cases, what conclusion can be drawn. A.A cartridges have not been fired from a weapon B.B cartridges have not been fired from a weapon C.Both A & B have been fired D.Neither A nor B have been fired AB

A submitted firearm will be fired several times using a water tank, boxes of cotton, or tubs of gelatin to obtain standards from the firearm. Standards Comparison

#9 Standards for bullets and cartridge casings are obtained by: A.Photography and casting B.Firing test bullets into water, cotton, or gelatin C.Collecting evidence from the crime scene

Does the caliber of the bullet match caliber of the firearm? Do the rifling impressions on the bullet match the pattern in the barrel? Do the striation patterns match between the suspect bullet/barrel and the standard bullet/barrel? Comparison Microscope

A – CS bullet B – Std. bullet #10 Given the image of the bullets above, what conclusion can be drawn. A.Bullets A & B were fired from the same weapon B.Bullets A & B were fired from different weapons