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