Forensic Ballistics and Firearm Examination Notes

Forensic Ballistics and Firearm Examination

Introduction

Robin Buller, a Brevet Sergeant with the Forensic Response Section, discusses forensic ballistics, including ammunition, firearms, and their examination in both crime scenes and the lab.

Overview of Forensic Ballistics

Laboratory Work

  • Classification of firearms according to the Firearms Act of South Australia.

  • Determining if ammunition is suitable for submitted firearms.

Scene Work

  • Analyzing shooting incidents (police shootings, homicides, suicides, drive-by shootings).

  • Trajectory analysis to determine the shooter's location.

Ammunition

Components

  • Case

  • Primer

  • Propellant

  • Bullet

Types

  • Centerfire: Primer in the center of the cartridge.

  • Rimfire: Primer around the outside base of the cartridge.

  • Shotshell: Center primer, used in shotguns.

Cartridge Case Materials

  • Aluminum

  • Plastic

  • Brass

  • Coated steel (armor-piercing ammunition)

Bullets

  • Plain lead

  • Jacketed (copper or brass)

Propellant

  • Slow burning, fast burning, or neutral.

  • Ignited by the primer.

Shotgun Ammunition

  • Contains multiple projectiles instead of a single bullet.

Caliber

Definition

  • Describes the bore of the firearm barrel.

  • Expressed in inches (e.g., .22.22 caliber) or millimeters (e.g., 9 mm×199 \,\text{mm} \times 19).

Naming Conventions

  • Based on bullet diameter, manufacturer, year of production, cartridge case length, or propellant amount.

Examples

  • 9 mm9 \,\text{mm} Parabellum: bullet diameter (9 mm), Parabellum being the manufacturer.

  • 7.62×397.62 \times 39: Military designation.

  • .30−06.30-06 Springfield: Caliber (.30), year produced (1906), and location (Springfield).

Shotgun Gauges

  • Based on weight division, not length.

  • 12 gauge is most common.

  • Refers to the number of lead pellets that fit the bore and equal one pound.

Ammunition Identification

Head Stamps

  • Indicate ammunition type and manufacturer (e.g., Winchester).

Measurements

  • Case diameter, length, shoulder, neck, and rim measurements.

Standards

  • Using SAMI (Sporting Arms and Ammunition Manufacturers' Institute) standards for verification.

Head stamp examples

  • Winchester (X), Remington, CCI (C)

Centifier headstamps

  • 6.5×356.5 \times 35 PMC, .38 special Winchester, .40.40 Smith & Western (Federal).

Shotshell Headstamps

  • Can be difficult to trace; may only indicate gauge (e.g., 20) with stars.

Wildcat Cartridges

  • Handmade or modified cartridges by non-commercial gunsmiths or hunters.

  • Customized for specific needs.

  • May originate from commercially made ammunition.

  • Importance: Head stamps may be misleading (e.g., .223 Remington).

Reloading

  • Replacing primer and propellant in a used cartridge case.

  • Cost-saving but time-intensive.

  • Potential safety issues if not done to SAMI standards.

Firearms

Key Knowledge Areas

  • Types of firearms.

  • Actions.

  • Barreling and rifling techniques.

  • Safety procedures.

  • disassembly and reassembly.

  • Manufacturer's marks, proof marks, and identifying marks.

  • Safety mechanisms.

  • Modified firearms.

  • Serial number restoration.

  • Suppressors/silencers.

Examination Purpose

  • Classifying firearms per the Firearms Act of South Australia (2015).

  • Determining functionality of safety mechanisms.

  • Test firing for national database (similar to fingerprint/DNA databases).

Firearm Types

  • Rifles

  • Handguns

  • Shotguns

  • Homemade/modified firearms

  • Black powder (antique firearms)

Homemade Firearms

  • Often constructed from hardware store materials (e.g., PVC piping).

  • Vary in sophistication and functionality.

Converted Blank Firing Firearms

  • Attempts to convert blank firing guns into live firing guns.

  • Modifications include changing the hammer, replacing the barrel, and drilling out obstructions.

Torch Firearms and Pen Guns

  • Concealed firearms disguised as everyday objects.

Firearm Actions

  • Single shot bolt action rifle: Manual reloading required after each shot.

  • Bolt action repeater: Automatic loading from a magazine.

  • Self loading/semi automatic rifles: Continuous firing with each trigger pull if ammunition is available.

  • Pump action: Manual slide movement to load and unload.

Handguns

  • Self loading Pistols: Semiautomatic action; popular among outlaw motorcycle gangs.

  • Revolvers: Single action (manual cocking) and double action (trigger cocks the hammer).

Shotguns

  • Break action: Manual opening for loading.

  • Pump action: Tubular magazine; similar action to rifles.

  • Self loading: Automatic loading with each trigger pull.

Colt AR-15

  • Self loading rifle used in massacres.

  • High capacity magazines.

  • Available in military (5.56 mm) and civilian (.223) versions, which are interchangeable.

Firearm Parts
Rifle

  • Barrel, forestock, magazine, trigger, butt, shoulder stock, bolt.

Revolver

  • Barrel, frame, grip, trigger, cylinder, hammer.

Self Loading Pistol

  • Includes a slide that actions the firearm.

Self Loading Pistol Action

  • Magazine under spring tension feeds rounds.

  • Slide recoils backward, ejecting the spent cartridge case via an extractor and ejector.

  • The next round pops up, and the slide chambers it during its forward movement.

  • Firing pin ignites the primer, propellant burns, and gases propel the bullet.

Gunshot Residue (GSR) and Sooting

GSR

  • Requires lead, barium, and antimony.

  • Comes from propellant, lubricant, and primer.

Sooting

  • Carbonous material from gas combustion.

Collection

  • Sticky stubs used to collect particles from hands or clothing.

Time Constraints

  • GSR collection is most effective within four hours.

  • Washing hands or putting hands in pockets dislodges particles.

Shotgun Discharges

  • Large amount of propellant.

  • Projectiles held by a wad.

  • Projectiles disperse with distance.

Rifling

  • Rifles and handguns have rifled barrels (grooves and lands).

  • Shotguns have smooth bores.

  • Rifling spins the bullet for stability and accuracy.

Identification

  • Striae matching can identify a bullet fired from a particular firearm.

Scene Investigation

Evidence Collection

  • Spent cartridge cases

  • Spent projectiles

  • Shotgun wads

Comparison Microscope Work

  • Matching cartridges and bullets.

  • Breech face marks (e.g., rectangular marks from Glocks).

  • Firing pin impressions.

  • Individual striae marks.
    *

Shooting Scene Reconstruction

  • Using string lines and probes to determine bullet trajectories.

Ricochet Marks

  • Lead splash indicates the angle of impact.

Glass Fractures

  • Radial and concentric fractures used to determine the order of shots.

Gunshot Wounds

Bullet Types

  • Lead, jacketed, hollow point, ballistic tip.

  • Hollow points deform upon impact, increasing injury.

  • Ballistic tips enhance aerodynamics.

Entry Wound Characteristics

  • Smaller, circular hole.

  • Inward beveling on the bone.

  • Charring and tattooing from burnt propellant.

  • Stippling
    *

Exit Wound Characteristics

  • Typically larger with irregular shape.

High Powered Caliber Rifles

  • Cause satellite tearing (star like pattern) due to gases.

Shotgun Wounds

  • Close range: single entry point with wad present.

  • Intermediate range: pellet dispersal pattern.

X-rays and MRIs

  • Used to examine deceased.

  • Lead snowstorming phenomenon with shotgun pellets.

  • Pellets can travel in blood vessels. MRIs shows bone impacts

Range Determination

  • Easier post mortem when the area is cleaned and shaven.

  • Bruising and abrasion marks.

  • Barrel brushing marks (match to a potential firearm)

Despite the general assumptions exit wounds are sometimes hard to tell from entry wounds without MRI's and thorough cleaning.