Ballistics quiz

Firearm identification includes

• Bullet comparisons

• Knowledge of weapons

• Restoration of removed serial numbers

• GSR characterization (garments & skin)

• Muzzle to target estimations

Bullet comparisons

• Each gun has its own inner surface markings

• The inner surface markings score the bullet as it leaves the barrel

• Test fire a bullet & compare markings

• If there is a match, you have the gun/suspect

• Individual characteristic

The barrel of a gun

• Made from a single bar of steel

• The bar is drilled out

• The inner surface after drilling leaves irregular random striations (no two barrels are the same)

• The inner surface is impressed with spiral grooves known as rifling

• There are several techniques for rifling (Button, Mandrel, etc.)

Lands

The original bore between two grooves

Caliber

• Distance between two grooves

• Recorded in hundredths of an inch or mm

• Caliber measurements are not an exact number

• mm → caliber (in): _ mm x (1 cm/10 mm) x (1 in/2.54 cm)

Determining the numbe rof lands and grooves from a bullet

1. Know the caliber

2. Measure the groove impressions

3. Measure land impression

   1. Calliber/(groove + land diameter) x 3.14

Types of bullets

1. Wad cutter

   1. Jacketed

   2. Plain lead

2. Hoxie

         - Ball at end to increase fragmentation

3. Jacketed flat nose

4. Round nose

5. Hollow tips

6. Talons

          - Spread open like the talons of an eagle

Metal jacket of a bullet

Usually copper

Armor piercing

• Teflon jacket

• Tungsten tip

• 45 caliber

Cartridge casings

• Pull the trigger of a gun and:

       1. Firing pin strikes the primer

       2. Ignites the powder

3. Gas expansion

4. Propels the bullet forward

• As the bullet moves forward the casing moves backward with an equal force

• Strikes the breech block marking the casing

• The shell is marked by the firing and loading mechanisms

• The firing pin will mark the primer uniquely

• The firing pin is a class characteristic

• The breechblock markings are an individual characteristic

On a cartridge bottom

1. Date

2. Brand

3. Caliber (arsenal)

4. Primer

Cartridge casings

1. Semiautomatic

- No lip at the base of the cartridge

2. Revolver

- Has a lip on the base of the cartridge

• The firing pin is a class characteristic

• The breechblock is an individual characteristic

Integrated ballistic identification system (IBIS)

• Automated firearm search system

  • Contains more than 800,000 images of:

    • Spent cartridges

    • Fire bullets

Distance determination

• Based on powder distribution

• Spread of powder

• Spread of shot

• Burn intensity on the skin

Gun shot residue (GSR)

• Found on the shooter

• Primer identification

• Most primers are lead, barium, and antimony based

• Found on the thumb web and back of hand

• GSR:

  • Palms

  • Back of the gun

  • Swab the hand with 5% nitric acid

  • Use AAS determine presence and concentration

  • SEM coupled with an x-ray analyzer

Serial number restoration

• Serial numbers are stamped into the metal with a high force

• Criminals grind, rifle, or punch out the serial numbers to avoid being tracked

• The force of the stamped numbers extend below the punched area and have stressed the metal

• Use an etching material

• Stressed area dissolves revealing the original numbers