Ballistics Intro to Firearms 1

Forensic Science: Fundamentals & Investigations, Chapter 17 2 Long Guns and Handguns o Long guns Rifles fire bullets Shotguns fire pellets (shot) or a single projectile (slug) o Handguns Pistols are fired with one hand Revolvers have a cylinder that holds usually six cartridges o Automatic and Semi-automatic

Forensic Science: Fundamentals & Investigations, Chapter 17 3 Firearms and Rifling o Grooves and ridges (lands) in the barrel of a gun produce the twisting that adds accuracy o This leaves a pattern on the bullet that is unique

Forensic Science: Fundamentals & Investigations, Chapter 17 4 Bullets, Cartridges, and Calibers o Cartridge—a case that holds a bullet, primer powder, and gunpowder o The bullet, usually of metal, is out front with the cartridge, holding the primer and propellant powders, behind.

Forensic Science: Fundamentals & Investigations, Chapter 17 5 How a Firearm Works 2. The primer powder sparks through the flash hole to the main propellant supply 1. The firing pin hits the base of the cartridge, igniting the primer powder

Forensic Science: Fundamentals & Investigations, Chapter 17 6 How a Firearm Works 4. The bullet follows the lands and grooves spiraling out of the barrel 3. The pressure of the explosion pushes the bullet from the casing into the barrel

Forensic Science: Fundamentals & Investigations, Chapter 17 7 Caliber of the Cartridge o Caliber—a measure of the diameter of the cartridge o In hundredths of an inch o Common calibers include.22,.25,.357,.38,.44, and.45 o Why should the caliber of ammunition match the firearm that shoots it? If they do not match, what could go wrong?

What is a bullet? o “Bullet” refers to the projectile(s) which actually exits the barrel of the gun when fired o Bullets vary in shape and composition o There exists hundreds of different types of bullets o Most types are variations on three main shapes & three basic compositions Forensic Science: Fundamentals & Investigations, Chapter 17 8

Anatomy of a bullet o The bullet (projectile) can be made of many different things o The primer powder initiates the contained explosion that pushes the bullet down the barrel. The primer is struck by the firearm’s firing pin that will strike the rim or bottom of the cartridge o The anvil and flash hole provide the mechanism of delivering the explosive charge from the primer to the gunpowder o The headstamp on the bottom of the cartridge casing identifies the caliber and manufacturer Forensic Science: Fundamentals & Investigations, Chapter 17 9

What are the types of bullets? Forensic Science: Fundamentals & Investigations, Chapter 17 10

Round Nose o Maximum penetration o Cheapest shape to manufacture o Easily loads into chambers Forensic Science: Fundamentals & Investigations, Chapter 17 11

Hollow Point o Spreads or mushrooms on impact o Causes additional damage to target o Inhibits penetration Forensic Science: Fundamentals & Investigations, Chapter 17 12

Wad Cutter o Used exclusively as a practice load o Minimizes penetration o Rips a hole in target paper which is visible by the shooter Forensic Science: Fundamentals & Investigations, Chapter 17 13

Bullet Composition: Three Types o Lead o ½ Jacketed o Jacketed (Full metal jacket) Forensic Science: Fundamentals & Investigations, Chapter 17 14

Lead Bullets o Cheap and soft o Dense o Easy to mold Forensic Science: Fundamentals & Investigations, Chapter 17 15

½ Jacketed o A lead bullet coated with copper half way up the exposed portion of the bullet o Used primarily for hollow points o Copper improves exit velocity o Lead promotes mushrooming Forensic Science: Fundamentals & Investigations, Chapter 17 16

Full Metal Jacket o A lead bullet completely coated in copper o Copper improves exit velocity o Used to hold the shape of the bullet in an effort to maximize penetration Forensic Science: Fundamentals & Investigations, Chapter 17 17

What Makes Fired Bullets Unique? o When a gun is fired, the barrel marks each bullet with its own unique pattern of land and grooves o By examining the lands and grooves, a bullet investigator can match to the gun from which it was fired Forensic Science: Fundamentals & Investigations, Chapter 17 18

What Makes Fired Bullets Unique (Cont’d)? o Investigators compare bullets and spent cartridge casings from a crime scene with bullets and spent cartridges shot from the suspected firearm Forensic Science: Fundamentals & Investigations, Chapter 17 19

What Makes Fired Bullets Unique (Cont’d)? o Firing pin marks left on the spent cartridge casings can also be used to identify a firearm Left on the bottom of the cartridge when the firing pin hits it to fire the shot o Breechblock markings are another kind of mark left on spent cartridge casings when the firearm is shot Causes explosive force that pushes the bullet forcasing backward against breechblock, which prevents the cartridge from shooting toward the user as it recoils Forensic Science: Fundamentals & Investigations, Chapter 17 20

Markings o Firing pin mark o Breechblock marking Forensic Science: Fundamentals & Investigations, Chapter 17 21

What Makes Fired Bullets Unique (Cont’d)? o Other marks left on spent cartridge casings include extractor and ejector marks Minute scratches produced as cartridge is placed in firing chamber (via extractor) and removed from chamber after firing (via ejector) Forensic Science: Fundamentals & Investigations, Chapter 17 22

Striations Forensic Science: Fundamentals & Investigations, Chapter 17 23

Matching Procedure for Striations o Fire bullets from a suspected weapon o With the aid of a comparison microscope, compare these “test fires” to the suspected bullets o Striations must be identical for a positive match Forensic Science: Fundamentals & Investigations, Chapter 17 24

Matching Procedure for Striations Forensic Science: Fundamentals & Investigations, Chapter 17 25