Forensic Science - Ballistics

What are the main features of a shotgun?

• Single or double barrel.

• Usually choked.

• Fired from the shoulder.

What is a “sawn-off” shotgun?

A shotgun with part of the barrel removed to improve concealment and increase spread of shot.

What are the key features of a rifle?

• Rifled barrel.

• Shoulder-fired.

• Fires bullets at long range.

What is an assault rifle?

A rifle with a shortened barrel that can be fully automatic.

What defines a pistol?

• Designed to be discharged by the hand.

• Short barrel.

• Short-range.

• Less accurate.

What is a sub-machine gun?

A pistol-type firearm fired two-handed with a longer barrel.

Usually fully automatic.

What is a revolver?

A pistol with a revolving cylinder containing multiple chambers.

What are the main components of ammunition?

• Case.

• Primer.

• Bullet.

• Propellant.

What chemicals are typically in primers?

• Lead styphnate (explosive).

• Barium nitrate (oxidiser).

• Antimony sulphide (fuel).

What are common propellants?

Nitrocellulose or nitrocellulose with nitroglycerine.

What are the 3 types of ballistics?

• Internal.

• External.

• Terminal.

What is internal ballistics?

Events from trigger pull to the bullet leaving the barrel.

What is external ballistics?

Bullet flight from barrel to target.

What is terminal ballistics?

What happens when the bullet hits the target.

What shape is a bullet trajectory?

Parabolic.

What features indicate close-range firing?

• Muzzle flash charring.

• Gas effects.

• Stellate tears.

• Tattooing from unburnt propellant.

At what range does tattooing typically occur?

Between 5cm and 30cm.

What are typical characteristics of a bullet entrance wound?

Usually circular, may have bullet wipe residue.

What are characteristics of exit wounds?

Larger, uneven, no external powder tattooing.

What does a shotgun wound look like up to 3m?

Usually a single hole, often square.

What happens beyond 3m?

Shot disperses and individual pellet “fliers” are visible.

What class characteristics can be determined from bullets?

Caliber and rifling (number of lands and grooves).

What class characteristics can be determined from cartridges?

• Caliber.

• Cartridge type.

• Firing pin.

• Extractor.

• Ejector marks.

What are lands and grooves?

Lands are raised areas.

Grooves are recessed spiral cuts in the barrel.

What is a firing pin impression?

An impressed mark from the firing pin striking the primer.

What are breech face marks?

Patterned or lined impressions left on the cartridge case base against the breech.