Ballistics

1. Ballistics

2. 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.

3. 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

4. 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.

5. 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.

6. 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.

7. 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

8. 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.

10. 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

11. 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.

13. 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.

15. 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.

17. 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.

18. 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.

19. 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.