Forensic Ballistics Overview

Forensic Ballistics

• Ballistics is the science of projectile motion and the conditions affecting it. It's an applied physics, evolving as modern civilization advances.
• A projectile is any object propelled from a firearm, metallic or non-metallic.
• Ballistics is not an exact science; it's a dynamic field subject to improvement.

Origin of the Word Ballistics

• Derived from the Greek words "ballo" and "ballein," meaning "to throw."
• Also associated with the Roman war machine, the Ballista, a giant catapult.

Scientific Instruments in Forensic Ballistics

Bullet Comparison Microscope

• Crucial tool in ballistics labs.
• Used to compare evidence bullets/shells with test bullets/shells to determine if they came from the same firearm.

Stereoscopic Microscope

• Preliminary examinations for fired bullets/shells, identifying class characteristics (relative distributions).
• Used for examining altered serial numbers on firearms.

Bullet Recovery Box

• Used in test firing to recover bullets and cartridge cases for comparison with evidence.

Helixometer

• Measures the "pitch of riflings" in firearms.
• Rifling pitch is the distance a bullet travels in one complete 360-degree rotation within the barrel.
• Often used in advanced ballistics labs or commercial agencies.

Analytical/Torsion Balance

• Weighs bullets/shotgun pellets to potentially determine firearm type, caliber, and make.

Ooscope

• Small instrument for examining a gun barrel's internal surface.
• Tiny lamp inserted for internal viewing.

Taper Gauge

• Used to identify firearm bore diameter.

Electric Gun Marker

• Used in labs to mark bullets, shells, and firearms.

Chronograph

• Measures bullet speed (muzzle velocity).

Shadowgraph

• Contains microscopic lenses for examining fired bullets/shells, determining class characteristics for orientation purposes.
• Features a large circular ground glass.

Projectile Motion

• Projectile motion is categorized into:
  • Direct Motion: The forward motion of the bullet caused by expanding gases from burning gunpowder.
  • Rotatory Motion: The bullet's rotation as it travels through the rifled barrel (twisted left or right).
  • Translational Motion: The bullet's movement after hitting a target, potentially causing ricochet.

Branches of Ballistics

• Early ballistics was divided into:
  • Internal (or Interior) ballistics
  • External or Exterior ballistics
  • Terminal ballistics
• Modern ballistics includes forensic ballistics, addressing firearm-related crime investigations.

Internal Ballistics

• Focuses on the projectile's motion inside the firearm:
  • Firing pin striking primer
  • Primer mixture ignition
  • Gunpowder/propellant combustion
  • Heated gas expansion
  • Pressure development
  • Energy generation
  • Gun recoil
  • Bullet velocity within the barrel
  • Bullet rotation within the barrel
  • Marks/cavities engraved on the bullet
• Land: elevated portion of the barrel
• Grooves: depressed portion of the barrel

Misfire vs. Hang-Fire

• Misfire: Failure of a cartridge to explode after firing pin impact
• Hang-fire: Delayed explosion of gunpowder after firing pin impact.

Exterior Ballistics

• Examines projectile motion after leaving the firearm's muzzle:
  • Muzzle blast (loud bang sound)
  • Muzzle energy (energy after leaving the firearm)
  • Trajectory (bullet's flight path)
  • Range (distance between firearm and target)
  • Effective range
  • Accurate range
  • Maximum range
  • Velocity (bullet speed)
  • Air resistance
  • Gravity's pull
  • Penetration
  • Gyroscopic Stability (rotating motion of bullet)
  • Yaw (wobbling motion due to uneven pressure)
  • Bullet drop vs. gravity
  • Bullet fired upward: velocity remains mostly the same on descent (unless air resistance is significant).

Terminal Ballistics

• Studies the bullet's effects on the target:
  • Terminal accuracy (bullet grouping size)
  • Terminal energy (bullet's energy)
  • Terminal velocity (bullet's speed)
  • Terminal penetration (bullet's depth of impact)
• Types of damage caused by bullets.