Firearms Identification

Firearms Identification Was a bullet or cartridge was fired by a particular weapon?

3 Areas of Interest Internal ballistics What happens when the gun is fired? External ballistics What happen to the bullet and residues outside of the gun? Terminal ballistics Where did the bullet go? Internal ballistics - Firing pin marks, spiraling marks External ballistics – direction and velocity of shot Terminal ballistics - Trajectory, speed, ricochet, penetration of objects, tissue damage

Anatomy of a Bullet Cartridge Case Lead Bullet Primer Gun Powder Cartridge case is weaker than the bullet

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

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

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

Breech 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.

Broach Cutter Broach – tool that goes through and cuts the pattern in the barrel (How you can tell the manufacturer) used to create rifling impressions in a barrel.

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

https://www.youtube.com/watch?v=OubvTOHWTms

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

#2 What is the benefit of using a firearm that is rifled? The bullet will be fired with greater accuracy The bullet will be fired faster The bullet will not be damaged when fired Think about how a football is thrown!

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.

Rifling Impressions on a Bullet -A) Land impression Barrel -A) Land -B) Groove B A Rifling Impressions on a Bullet -A) Land impression -B) Groove impression Remember that the barrel rifling will leave a REVERSE IMPRESSION on the lead bullet! A B B

#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. True False

#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. True False There will be minute differences that can be seen through microscopic analysis.

B A A) Land impression B) Groove impression Notice that lands in the barrel scrape away the bullet, while grooves in the barrel leave the bullet intact. B A

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

#4 Given the image of the bullet below, what conclusion can be drawn. This bullet has not been fired from a weapon This bullet was fired from a rifle or handgun. This bullet was fired from a shotgun. The rifling pattern means it couldn’t have been fired from a smooth-barreled gun like a shotgun.

Caliber - the diameter of the bore of a rifled firearm 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 Measure the diameter from the narrowest part to the narrowest part.

#5 Caliber is measured from: Land to groove Land to land Groove to groove

#5 Caliber is measured from: Land to groove Land to land 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 Another class characteristic of rifling that is seldom comes into play is the rate of twist or pitch of the rifling in the barrel.  The rate of twist is the distance the rifling needs to spiral down the barrel for it to complete a single revolution.  An example would 1 turn in 12 inches.  The term pitch refers to the angle at which the rifling is cut in the barrel.  The bottom clearly has more pitch than the top

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. No two gun barrels have the exact same markings. These markings leave unique striations or impressions on a bullet. This allows a bullet to be traced back to a particular firearm.

Bullet Individual Characteristics It is possible to determine the bullet on the left and the bullet on the right are from the same gun by matching the striations. See examples A and 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 Another class characteristic of rifling that is seldom comes into play is the rate of twist or pitch of the rifling in the barrel.  The rate of twist is the distance the rifling needs to spiral down the barrel for it to complete a single revolution.  An example would 1 turn in 12 inches.  The term pitch refers to the angle at which the rifling is cut in the barrel.  The bottom clearly has more pitch than the top

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 Cartridge

Firing Pin Marks In order to fire the cartridge, the primer must first be ignited. To accomplish this a firing pin strikes the center ring of the cartridge. This will in turn leave a distinct impression that is unique to the firing pin of that particular gun.

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

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

Standards Comparison 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.

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

Comparison Microscope 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?

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