Csi training : Toolmarks and

CSI TrainingFirearms and Toolmarks

STEM: CSI Experience Activity Supplemental Notes

CSI-Firearms and Toolmarks

• Parts of a Gun


• Semiautomatic Handgun: A gun that fires a single cartridge, ejects spent cartridge case, and reloads itself each time the trigger is pulled. A separate trigger pull is required each time the weapon is fired.


• Barrel: A long tube the bullet or projectile travels through before it exits the firearm.

– The barrel has many shallow ridges, called rifling, which helps the bullet fly in a straight line.


• Cartridge Case: A container for all the other parts of a cartridge- the projectile, primer, and propellant (gunpowder). After the bullet has been fired the “spent” or empty cartridge case is marked with that gun’s unique individual characteristics.


• Slide: The portion of a semiautomatic firearm that holds the firing mechanism. After the bullet is fired the slide moves backwards to eject the used cartridge and automatically load another.


• Firing Pin: The part of the firearm that hits the primer in a cartridge and causes it to explode. This initiates the firing of the bullet. The firing pin can leave distinct marks on the cartridge case.


• Magazine: A device which holds the cartridges and feeds them one at a time into the firing chamber of the firearm.


• Rifling: Spiraling ridges located inside the barellof the gun. They cause the projectile to spin as it flies through the air, which improves accuracy. The rifling also marks the bullet with the gun’s unique characteristics.


HOW A GUN WORKS

• When the trigger is pulled.

• The hammer hits the firing pin.

• The firing pin hits the cartridge.

CSI-Firearms and ToolmarksPARTS OF A CARTRIDGE

• Cartridge: A single unit of ammunition made up of a projectile, propellant , and primer, surrounded by the cartridge casing. A “blank” is a cartridge without a projectile.


• Primer: A shock sensitive chemical mixture that explodes when struck by the firing pin. Sparks form the primer ignite the propellant and initiate firing of the bullet.


• Cartridge Case: A container for all the other parts of the cartridge, the projectile, primer, and propellant (gunpowder). After the bullet has been fired the “spent” or empty cartridge is marked with that gun’s unique individual characteristic.


• Smokeless Gunpowder: A complex chemical mixture that rapidly burns when ignited by a spark from the primer. This produces gases that rapidly expand and force the bullet out of the firearm.


• Caliber: An approximate measurement of the bullet’s diameter. For example, a .45 caliber bullet has a diameter of 0.45 inches, and a 9mm bullet has a diameter of 9 millimeters. (0.9 centimeters)


• Projectile: Any object propelled by an explosive reaction. Bullets are specialized projectiles designed to be fast and accurate. The size of the bullet is measured by its caliber (diameter).

CSI-Firearms and ToolmarksBullet Characteristics

• Stirations: Tiny, microscopic scratches on the surface of the bullet, usually located inside the rifling impressions. No two firearms will produce exactly the same pattern of striations.


• Rifling Impression: Impressions left on the surface of the bullet after it has been fixed from a firearm with a rifled barrel. The rifling impressions on a bullet can be either conventional (deep and easy to see, as in the picture) or polygonal (smoother and harder to see)


• Rifling Number: The number of lands (raised areas) or grooves in a rifled barrel. The rifling number of a particular firearm can be determined by rotating the bullet and counting the number of rifling impression present on the surface.


• Rifling Direction: Rifling grooves can spiral either to the left or right; making the bullet spin either clockwise or counterclockwise in the air. The direction of the rifling is determined by the direction of the grooves as they move from the base to the top of the bullet.


• Firearms Examiners use two types of bullet characteristics to determine if a bullet could have been fired by a certain gun:

• What would not be a class characteristic??

• Striations, caliber, Rifling Direction, or Rifle Number

• Class Characterisitcs: Specific for a certain brand or type of firearm.

• Individual Characteristics: Specific for an INDIVIDUAL firearm.

CSI-Firearms and ToolmarksClass Characterisitics

• Firearms Examiners use two types of bullet characteristics to determine if a bullet could have been fired by a certain gun:

• Class Characterisitcs: Specific for a certain brand or type of firearm.

• Individual Characteristics: Specific for an INDIVIDUAL firearm.

Csi training : Toolmarks and

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