Chapter 17 Ballistics Introduction

1. Chapter 17 Ballistics Introduction Ballistic evidence helps explain: • What type of firearm was used. • The caliber of the bullet. • Internal diameter of a gun barrel • The number of bullets fired. • Where the shooter was. • Whether a weapon was fired recently. • If a firearm was used in previous crimes.

2. History of Gunpowder and Firearms • The Chinese invented gunpowder over a thousand years ago. • In the beginning, wicks were used ignite the gunpowder. • The cartridge loading followed. • Rifling provided greater accuracy. • Revolver, semi-automatic, and automatic handguns were developed. Forensic Science: Fundamentals & Investigations, Chapter 17

3. Firearms and Rifling • Grooves and ridges (lands) in the barrel of a gun produce the twisting that adds accuracy. • This leaves an individualized pattern on the bullet.

4. Bullets, Cartridges, and Calibers Bullets and cartridges are packaged together. The bullet, usually of metal, is out front with the cartridge, holding the primer and propellant powders, behind.

5. How a Firearm Works • The firing pin hits the base of the cartridge, igniting the primer powder. • The primer powder sparks through the flash hole to the main propellant supply. • The pressure of the explosion pushes the bullet from the casing into the barrel. • The bullet follows the lands and grooves spiraling out of the barrel.

6. Caliber of the Cartridge • Caliber is a measure the diameter of the cartridge. • These usually are hundredths of an inch. • Very, very specific! • Common calibers include .22, .25, .357, .38, .44, and .45.

7. Matching lands (elevations) Matching grooves (indentations) The Study of Bullets and Cartridge Casings • How is each fired bullet marked? As a gun is fired, the barrel marks each bullet with its own unique pattern of lands and grooves. 2. What is the procedure to match a spent bullet to the firearm that shot it? Investigators compare bullets and spent cartridges shot from the suspected firearm. To get a known bullet for comparison, they test-fire the weapon. • What makes up a test-firing, and why is it done? Investigators test-fire the weapon into a water tank or gel block. This captures the bullet without damaging it. Then, they can compare the markings on known bullets with those on the suspect bullets.

8. Gunshot Residues • Particles of unburned powder and traces of smoke are the residues of gunshots. • They can leave a trace on the hand, arm, face, hair, or clothing of the shooter. • They can also leave a trace on the victim. • Chemical testing often can detect residue even if removal is attempted. • The distance from the victim to the shooter can be determined by examination of the residue pattern on the victim. Forensic Science: Fundamentals & Investigations, Chapter 17

9. Wind shield Distance along path of bullet to window, 23.9” Path of bullet x y 60 feet Horizon Distance along horizon to window, 23.5” Trajectory • Two reference points are needed to define the trajectory. • Investigators can figure the shooter discharged the firearm somewhere along that line. Forensic Science: Fundamentals & Investigations, Chapter 17

10. Trajectory • Reference points can be bullet holes in objects or victims. • An entry point and exit point on a victim can be used. • Gunshot residue or spent cartridge casings can be less specific reference points. • Investigators can use lasers to trace a straight-line path to help determine the position of the shooter. Forensic Science: Fundamentals & Investigations, Chapter 17

11. Bullet Wounds • Why do entrance wounds tend to be smaller than exit wounds? –The size of the entry should be smaller than the bullet because skin in somewhat elastic. Exit wounds are generally larger because as the bullet moves through the body, it may collect and carry body tissue and bone with it. • If the bullet penetrates clothing, what can fibers embedded in the wound indicate? Fibers imbedded in wounds can indicate the direction of entrance. • Where is gunshot residue usually found? Gunshot residue can be found only around entrance wounds • If the gun is fired with the muzzle touching the victim’s skin, what telltale mark may show up? The hot gases released from the muzzle flash may burn the skin. • Will larger or will smaller caliber bullets tend to lodge within the body rather than passing through? Why? High-speed bullets are more likely to pass through a body. Therefore, small-caliber bullets, such as a .22 caliber, tend to lodge within the body, while larger-caliber bullets will pass through.

12. Final • The final exam will be: • 20 multiple choice coming from this power point. (40 points) • A reading with 20 questions (40 points) • 80 points in total Forensic Science: Fundamentals & Investigations, Chapter 17