Firearms and Ballistics Notes

Firearms and Ballistics

Firearm Safety

  • Always wear hearing protection.

  • You have to protect them because they won’t protect you.

Types of Forensic Firearms Evidence

  • Firearms

  • Cartridges

  • Projectiles (Bullets)

  • Cartridge Casings

  • Ballistic Impact Marks (BIM)

  • Gunshot Residue

Firearm Types

  • Handguns

    • Derringer

    • Revolver: The cylinder rotates and brings the cartridges to the barrel

    • Semi-Automatic (Automatic)

  • Rifles

  • Shotguns

  • Machine Guns

Forensic Ballistic Analysis

  • Internal Ballistics

    • Interaction of firearm mechanical properties and ammunition.

  • External Ballistics

    • Forces which act upon a bullet in flight.

  • Terminal Ballistics

    • Forces which act upon a bullet striking a target.

  • GSR is a transition from External Ballistics to Terminal Ballistics.

Internal Ballistics

  • How is caliber measured?

    • Caliber is measured by the size of the bore in the barrel of the firearm.

      • True measurement of caliber is across the BORE of the barrel!!

    • Caliber is also a measure of the diameter of the base of the bullet. Bullets are measured in hundredths (or thousandths of an inch).

    • A .45-caliber bullet measures 45/100 of an inch in diameter (almost 1⁄2 inch).

    • European naming of firearm caliber uses the metric system for measurement of bullet diameter.

    • Proper terminology for caliber comes with experience.

  • What is caliber? The term used to describe the size of a bullet (and cartridge) which will be discharged from a firearm. Measured in 100ths of an inch or millimeters (mm).

  • What can be determined from bullets?

    • The weight of a deformed bullet will include or exclude certain types of firearms.

    • The rate of twist of the bullet will include or exclude certain types of firearms.

    • Two or more “Rate of twist” impressions on severely deformed bullets can provide overall caliber and certain classifications for a bullet.

    • If the bullet is not deformed, the diameter can be measured or compared with known caliber bullets.

  • What is ammunition (a cartridge) composed of?

    1. Bullet.

    2. Case.

    3. Powder.

    4. Primer.

    • On occasion, you will see the “bullet” listed as the “projectile.” The “powder” is also called “propellant.”

Internal Ballistics Headstamp Markings

  • The greatest amount of forensic information for the cartridge casing to be tested and compared to a database of other cartridge casings is the firing pin mark.

  • IBIS, much like AFIS, does NOT match the casing. It provides a list of known close matches.

Internal Ballistics Cartridge Case Markings

  • CUT-OUT MARK

  • MAGAZINE MARK

  • BREECHFACE MARK

  • BREECHFACE MICROSTAMP

  • FIRING PIN DRAG MARK

  • FIRING PIN IMPRESSION

  • FIRING PIN MICROSTAMP

  • FIRING PIN APERTURE MARK

  • EJECTOR MARK

  • EJECTION PORT MARK

  • CHAMBER STRIATIONS

  • EXTRACTOR OVERRIDE & GOUGE MARKS

Internal Ballistics Breakdown of a Semi-Automatic Firearm

  • Extractor: An extractor is an action component that serves to remove spent casings of previously fired cartridges from the chamber and ensure the smooth operation of the firearm. It works by gripping the casing and pulling it out as the action cycles.

  • Ejector: The ejector is responsible for expelling the spent cartridge casing from the firearm after firing, ensuring that the firearm can cycle and load the next round efficiently.

Internal Ballistics Comparison Microscope

  • Land and Groove Impression

  • Land and Groove Impressions 10x

  • 40x magnification of rifling impressions on the side of a 9mm bullet.

  • Musket Ball Effect: The musket ball effect occurs when the grooves in the barrel engage the projectile, leading to a more stable and accurate flight path, which enhances the overall ballistic performance of the round.

    • Non-rifled barrel. May not form a good seal between the bullet and the barrel.

    • Rifled barrel. Tight seal between bullet and barrel.

External Ballistics

  • What forces act upon a projectile in flight?

    • Lift initially balances gravity.

    • Velocity overwhelms drag upon discharge.

Bullet Spin in Flight

  • What path do bullets travel in?

    • It is NOT a straight line!!

    • A bullet’s path is a parabola (or parabolic)

External Ballistics-GSR

  • Gunshot Residue (GSR) is the term given to the discharge of gunpowder and primer components which are pressed out of a firearm when fired.

    • Composed of a mixture of burned powder, unburned powder, and primer components.

    • Detection for barium, lead, and antimony are common in GSR testing.

  • GSR Discharge Plume- Semi-Automatic

  • GSR Discharge Plume- Revolver

External-Terminal Ballistics (GSR)

  • GSR is the transition of external ballistics to terminal ballistics.

  • GSR can be used to detect “muzzle to target” distance at short ranges.

  • The GSR plume at close quarters is considered to be like a fingerprint to each individual firearm and ammunition type.

Terminal Ballistics GSR

  • Hands are too close to the muzzle

  • Terminal Ballistics Cavitation Theory

    • Temporary Cavity

    • Permanent Cavity

  • Cavitation theory states a large temporary wound cavity caused by the impact and radial kinetic energy of a bullet striking the target.

  • This large cavity is temporary, and the surrounding material will be returned to its “normal” configuration.

  • The permanent wound cavity is much smaller in diameter.

  • Would need the gun suspect during the crime and any ballistic evidence collected at the scene to analyze the trajectory and caliber of the projectile. The residue will work up to 3-31/2 feet

Terminal Ballistics Secondary Combustion “Sonoluminescence"

  • Caused by a rapid change of pressure within the cavity.

  • GSR burns on a close-quarter contact bullet wound

Terminal Ballistics

  • Shooters tend to be AWFUL shots.

  • Bullets which are transmitted into lab analysis are rarely perfect.

  • Analysis can still be performed.

  • Bullets are often the gateway to other criminalistic evidence.

  • Bullets can act like vacuum cleaners and suck up pieces of substrate they interact with.

  • Bullets passing through garments can acquire fibers.

  • Bullets passing through paint can acquire paint samplings.