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Ballistics

Chapter 17. Ballistics. Ballistics. The study of bullets & firearms Ballistic evidence answers questions: Type of firearm used Caliber of bullet Number of bullets fired Location of shooter Angle of impact If firearm has been used before. History of Firearms.

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Ballistics

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  1. Chapter 17 Ballistics

  2. Ballistics • The study of bullets & firearms • Ballistic evidence answers questions: • Type of firearm used • Caliber of bullet • Number of bullets fired • Location of shooter • Angle of impact • If firearm has been used before

  3. History of Firearms • Gunpowder was invented by the Chinese over 1000 years ago, and used for fireworks and rockets. • 14th century Europeans figured out how to make the earliest guns .

  4. Antique Guns - Muzzle Loaders • Matchlock gun (above) & flintlock gun (below)

  5. Modern Guns – Percussion Firing • Modern guns use a cartridge: • Projectile (bullet or shot) • Primer – ignites when struck by hammer of gun • Gunpowder • Anvil and flash hole – delivers explosion from primer to gunpowder • Casing – contains everything • Rim & headstamp – identifies caliber & manufacturer

  6. Caliber of a Bullet • Bullets are named by caliber and length. • Caliber is the diameter in inches Ex: .44 caliber = 44/100 of an inch • In Europe, metrics are used Ex: 9 mm • Caliber of the bullet matches the caliber of the gun.

  7. Gauge of a Shotgun • Shotgun shells are measured in gauge – the number of round lead balls per pound. • Smaller gauge numbers mean larger shot. • Gauge of the shell matches the gauge of the gun.

  8. How a Firearm Works • Pulling the trigger causes the firing pin of the hammer to hit the cartridge, igniting the primer. The primer delivers a spark through the flash hole, igniting the gun powder. The gunpowder explodes, driving the bullet down the barrel and out of the gun.

  9. Firearms and Rifling • Lands and grooves leave marks on bullets called rifling patterns.

  10. Matching Rifling Patterns • Because no two guns are identical, each gun leaves a unique rifling pattern. • Investigators test-fire suspected weapons into a water tank or gel block to get an undamaged bullet for comparison.

  11. Matching Rifling Patterns • The lands and grooves (also known as striations)of the test-fired bullet are then compared under a comparison microscope with the bullets and casings from a crime scene.

  12. Matching Cartridge Casings • Marks used to match cartridges to a gun: • Firing pin marks • Breechblock marks - created when the gun leaves an impression on the cartridge as it stops it from moving toward the shooter. • Ejector marks – created when a cartridge is automatically ejected from a gun

  13. NIBIN • NIBIN (National Integrated Ballistics Information Network) is a searchable database of bullet and cartridge markings recovered at crime scenes.

  14. Gun Shot Residue (GSR) • Gunpowder is made of potassium nitrate, sulfur and charcoal. • Gunshot residue (GSR) lands on the shooter, victim, and surrounding areas during a shooting. • Scientists test for the presence of GSR.

  15. GSR • Distance between the victim and shooter can be estimated by looking at the GSR pattern on the victim.

  16. GSR • Investigators test for GSR in a location to recreate a crime scene. • The hands and clothing of suspected shooters are also tested.

  17. Determining Entrance and Exit Wounds • Entrance wounds are usually round and smaller than the bullet, and exit wounds are larger, and might be irregular shapes. • Fibers from clothing may show the direction the bullet traveled. • Only entrance wounds have GSR. • Some bullets may not exit the body – high speed bullets are more likely to. • Close range entrance wounds sometimes have a ring around them.

  18. Trajectory • The path of a fired bullet is the trajectory. • Affected by forward force of gun and gravity. • Used to determine location of shooter. • Need two reference points to calculate trajectory.

  19. Calculating the Trajectory • Law of Tangents:

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