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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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Presentation Transcript
  • 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
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 .
antique guns muzzle loaders
Antique Guns - Muzzle Loaders
  • Matchlock gun (above) & flintlock gun (below)
modern guns percussion firing
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
caliber of a bullet
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.
gauge of a shotgun
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.
how a firearm works
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.

firearms and rifling
Firearms and Rifling
  • Lands and grooves leave marks on bullets called rifling patterns.
matching rifling patterns
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.
matching rifling patterns1
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.
matching cartridge casings
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
  • NIBIN (National Integrated Ballistics Information Network) is a searchable database of bullet and cartridge markings recovered at crime scenes.
gun shot residue gsr
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.
  • Distance between the victim and shooter can be estimated by looking at the GSR pattern on the victim.
  • Investigators test for GSR in a location to recreate a crime scene.
  • The hands and clothing of suspected shooters are also tested.
determining entrance and exit wounds
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.
  • 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.