amc week 9 ballistics email
Post on 19-Nov-2014
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Firearms and Ballistics
Revolver
Semi-Auto Pistol
How a gun works
Four Components of Ammunition
• Primer
– Rimmed or Centerfire
• Cartridge Case or Shotshell
• Propellant
• Projectile(s)
Ammunition
Ammunition
PREMIUM LOAD with SHOTCUP
Pellets do notcontact bore
Some problems
Stable vs. Instable
Projectile Flight
Rifling
• When a firearm is manufactured, the individual parts are made with tools that are in a constant state of change
• As a result, no two guns will leave the same marks on the ammunition components
• The marks found on bullets are sometimes referred to as striations
The match on the bullet
Gunshot Residue
Source of Gunshot Residue
• Firing a weapon may cause microscopic particles of primer residue and gunpowder to be deposited on the hands of the shooter
• The higher the caliber, the more GSR depositied on hands
• .22 caliber rim-fire cartridges will sometimes not show traditional GSR particles
Primers
• Lead Styphnate– Primary explosive
• Barium Nitrate– Oxygen Source
• Antimony Sulfide– Fuel
Formation of the Particle
• Upon detonation, the compounds of the primer vaporize, mix and then condense back into particles
• The result: what was once three separate particles have become one particle made up of lead, barium and antimony
Inside a GSR kit
• Each GSR kit contains– Instructions– A pair of rubber gloves– Labels– Two sample vials
• Each vial contains adhesive coated aluminum stub mounted on the base of a rubber stopper
• Stub pressed and lifted on the surface being sampled– Hand – Face– Clothing
The Examination
• Look for particles with the proper morphology and size
• Look for particles which contain all three components of the primer– Lead (Pb)– Barium (Ba)– Antimony (Sb)
Scanning Electron Microscope
• Magnification ranges from 10x to 10,000x
• Allows you to visualize GSR particles and gives you information on the elemental makeup of the particles
GSR Particle on the SEM
Positive: What does it mean?
• The individual fired a weapon
• The individual handled a weapon right after it was fired
• The individual was very near when the gun was fired
• The individual touched a surface that had GSR on it.
• Etc, etc, etc.
Negative: What does it mean?
• The individual did not fire a weapon
• The individual washed their hands
• The sample was collected after the recommended 4-6 hour time window
• The individual was wearing gloves when they fired the weapon
• Etc, etc, etc.
Bullet Trajectory
Projectile Penetration
• Three Possibilities– Projectile is stopped by impact without
penetration– Projectile will penetrate the object without
exiting– Projectile will pass through object (Perforate)
Definitions
• PenetrationPenetration is when a projectile enters but does
not exit. Not to be confused with Perforation
• Perforation Perforation is when a projectile passes through
and through. Not to be confused with Penetration
Penetration and perforation
The Bullets effect on sheet metal at increasing angles
Critical Angle and Deflection
Critical Angle and Deflection
19
Trajectory reconstruction using lasers
20
Laser trajectory at night
Shotgun Pellet PatternsIn General…. For every 1” across
= 1 Yard from Muzzle
7”
Muzzle to Target = 7 Yards
Pellet Pattern Diameter vs. Range
Orthogonal Impacts
d d d
Non-Orthogonal Pellet Patterns
sin-1 (d/D) = incidence angle
Orthogonal StrikesNo. 4 Buck12-ga.
d = 7 in.
450 Incident Angle with No. 4 Buck, 12 ga.
d = 7 in.
d/D = 0.67Sin-1 = 420
Same Rangeas previous shot
LEFT vs RIGHT
RIFLING TWIST DETERMINATIONfrom
RICOCHET MARKS on SMOOTH, HARD SURFACES
The“Chisum”
Trail
230-gr. .45 Auto FMJ-RN Incident Angle = 100
Surface = Smooth Steel Ricochet Angle = 1.40
130
profile views
Three 50-gr. FMJ .25 Automatic BulletsRicocheted from a Hard, Unyielding Surface
after Low (less that 50) Incident Angle Impacts
Cartridge Case Ejection Patterns
• Each Firearm is Different – Ammunition– Ground Surface
• Shooter’s Stance Does Not Matter– Weaver vs. Prone– Grip doesn’t matter
• How the Gun is Held Matters
Ejection Patterns
X
Bullets and Glass
BB Impact
Effects of Projectiles on Common Materials
• Laminated
Glass
Laminated Auto Glass
What else can be matched?
Extractor and Breech
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