Chapter 17 Ballistics

Ballistics The study of bullets & firearms Ballistic 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

History of Firearms 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 .

Antique Guns - Muzzle Loaders Matchlock gun (above) & flintlock gun (below)

Modern Guns – Percussion Firing 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

Caliber of a Bullet Bullets are named by caliber and length. Caliber is the diameter in inches Ex: .44 caliber = 44/100 of an inch In Europe, metrics are used Ex: 9 mm Caliber of the bullet matches the caliber of the gun.

Gauge of a Shotgun 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.

How a Firearm Works Pulling the trigger causes the firing pin of the hammer to hit the cartridge, igniting the primer. The primer delivers a spark through the flash hole, igniting the gun powder. The gunpowder explodes, driving the bullet down the barrel and out of the gun.

Firearms and Rifling Lands and grooves leave marks on bullets called rifling patterns.

Matching 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.

Matching Rifling Patterns 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.

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

Gun Shot Residue (GSR) 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.

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

GSR Investigators test for GSR in a location to recreate a crime scene. The hands and clothing of suspected shooters are also tested.

Determining Entrance and Exit Wounds 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.

Trajectory 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.

Calculating the Trajectory Law of Tangents: