Chapter 17

The study of bullets & firearmsBallistic evidence answers questions:

Type of firearm used Caliber of bullet Number of bullets fired Location of shooter Angle of impact If firearm has been used before

Gunpowder was invented by the Chinese over 1000 years ago, and used for fireworks and rockets.

14th century Europeans figured out how to make the earliest guns .

Matchlock gun (above) & flintlock gun (below)

Modern guns use a cartridge: Projectile (bullet or shot) Primer – ignites when struck

by hammer of gun Gunpowder Anvil and flash hole – delivers

explosion from primer to gunpowder

Casing – contains everything Rim & headstamp – identifies

caliber & manufacturer

Bullets are named by caliber and length.

Caliber is the diameter in inchesEx: .44 caliber =

44/100 of an inch In Europe, metrics are used

Ex: 9 mmCaliber of the bullet matches the

caliber of the gun.

Shotgun shells are measured in gauge – the number of round lead balls per pound.

Smaller gauge numbers mean larger shot.

Gauge of the shell matches the gauge of the gun.

1. Pulling the trigger causes the firing pin of the hammer to hit the cartridge, igniting the primer.

2. The primer delivers a spark through the flash hole, igniting the gun powder.

3. The gunpowder explodes, driving the bullet down the barrel and out of the gun.

Lands and grooves leave marks on bullets called rifling patterns.

Because no two guns are identical, each gun leaves a unique rifling pattern.

Investigators test-fire suspected weapons into a water tank or gel block to get an undamaged bullet for comparison.

The lands and grooves (also known as striations)of the test-fired bullet are then compared under a comparison microscope with the bullets and casings from a crime scene.

Marks used to match cartridges to a gun: Firing pin marks Breechblock marks - created when the

gun leaves an impression on the cartridge as it stops it from moving toward the shooter.

Ejector marks – created when a cartridge is automatically ejected from a gun

NIBIN (National Integrated Ballistics Information Network) is a searchable database of bullet and cartridge markings recovered at crime scenes.

Gunpowder is made of potassium nitrate, sulfur and charcoal.

Gunshot residue (GSR) lands on the shooter, victim, and surrounding areas during a shooting.

Scientists test for the presence of GSR.

Distance between the victim and shooter can be estimated by looking at the GSR pattern on the victim.

Investigators test for GSR in a location to recreate a crime scene.

The hands and clothing of suspected shooters are also tested.

Entrance wounds are usually round and smaller than the bullet, and exit wounds are larger, and might be irregular shapes.

Fibers from clothing may show the direction the bullet traveled.

Only entrance wounds have GSR. Some bullets may not exit the body

– high speed bullets are more likely to.

Close range entrance wounds sometimes have a ring around them.

The path of a fired bullet is the trajectory. Affected by forward force of gun and gravity. Used to determine location of shooter. Need two reference points to calculate

trajectory.

Law of Tangents: