Ballistics

What is Forensic Ballistics Any projectile is considered ballistic evidence. These include bullets, arrows, objects launched from a slingshot etc. Most often the scientist is looking at bullets. The goal is to match a projectile with the weapon it came from. Each weapon uses a specific bullet and puts a specific type of mark on the bullet when it is fired.

The Gun Trigger – mechanical piece that the person pulls. Firing pin – pin that strikes the back of the bullet when the trigger is pulled igniting the primer. Bolt – the metal piece that moves forward and seals the bullet in the chamber. Breech – the back of the barrel that the bullet enters before firing. (chamber) Barrel – part that the bullet passes through after firing. Rifled with grooves to control the path of the bullet. Firing pistol

The Cartridge The cartridge has multiple parts. 1- the bullet which is the projectile 2- the case or shell – holds it together 3- the propellant (gunpowder) – provides chemical energy to accelerate the bullet. 4- the rim – holds it in the breach and provides a surface to grab to extract the bullet. 5- the primer. Ignites the propellant when struck.

Variations on a Theme All modern bullets work basically the same way. Shotgun shells have tiny ball bearings inside the plastic case that get released when the propellant is ignited. Caliber of the bullet refers to the diameter of the projectile it fires. 11.45mm = 0.45in, 9mm = 0.357in, 7.62mm = 0.30in, 5.56mm = 0.22in These bullet diameters can have different masses depending on their length. Bullets have different shapes in order to do maximum damage to the type of target it is going to be used against.

Stopping Power Refers to the ability of the projectile to cause enough damage to incapacitate a target where it stands. Not the same as lethality, which refers to its ability to kill a target. Related to the bullets velocity, mass, and shape. Shape determines how much energy is transferred to the target. Bullets that penetrate can pass through the target without slowing it down Bullets that expand transfer all energy to the target.

Bullet Velocity Muzzle velocity is the speed at which the bullet leaves the end of the barrel. After leaving the barrel, air resistance continues to slow the bullet down. Different shaped bullets are affected by the air differently. Guns meant for long-range targets have high muzzle velocities, while short-range guns have a lower velocity. The momentum of the bullet is related to stopping power. P=mv

Bullet Shapes Flat point – flat nose means more lead at the tip. Expand well. Good for soft targets. Round nose – round nose helps bullet travel in straight line. Good for soft targets. Spitzer – pointed nose – good for reducing drag which increases velocity and accuracy. Better for penetration of hard targets, tumbles on impact. Hollow point – opening in nose increases expansion. Good for soft targets. The bullet shape, velocity, and mass also determines stopping power.

Types of guns Handgun small gun able to be concealed and fired from one hand. Accurate at close range. Small caliber bullet. (9mm is most common) Good where space is limited and long barrels would be a disadvantage. (homes) Most common self defense weapon. Revolvers have 6 independent chambers and must be manually reloaded. Semi-automatics have a magazine that reloads automatically. Clips can be changed after 9-15 shots

The Shotgun The shotgun is also a good short-range weapon. Ball bearings spread out after firing. The more spread out, the less damage. Can be single-barreled or double-barreled. Both need to be reloaded by hand. There are semi-automatic and pump-action versions as well. For small spaces, the barrel can be sawed off. This keeps the bulky barrel from getting caught on things, but reduces its effectiveness at long range.

Submachine guns Smaller semi-automatic or automatic rifles. Low caliber in that they fire pistol cartridges. Low stopping power, but highly accurate and good for small spaces. Common for law-enforcement and special operations where house fighting is a possibility. Military uses carbines which are a little larger and have a better stopping power due to larger caliber bullets.

Rifles Long barreled, high muzzle velocity, very accurate, high stopping power, large caliber. Can be single shot bolt-action as in most hunting rifles. Some are semi-automatic. Assault rifles have a single shot, 3 shot burst, or full automatic setting and can hold 15 – 150 rounds depending on the size of the magazine.

Forensic Ballistics Experts can look at three different things. Firing pin mark on cartridge. Breech markings made by the metal scraping up against the cartridge during firing or ejection. Striations left on the bullet while passing through the rifled barrel.

The Best Evidence The type (caliber) of bullet narrows down the possibilities of the weapon. All other techniques require the weapon. Striations are unique to each rifle but can be deformed on impact and can’t be . The cartridge is the best evidence. The breech marks and the firing pin leave distinct marks called toolmarks that will not be damaged upon firing. Marks do change over time and can be modified by the owner.

Databases ABIS – Automated Ballistics Identification System is the software. IBIS – International Ballistics Identification Systems is the database. When a weapon is manufactured, a bullet is fired and entered into the database. All weapons used in a crime are entered into the database as well. Soon firing pins will stamp the cartridge with the make and serial number of the gun.