Forensic Ballistics Notes

Introduction

  • Robin Buller, Brevet Sergeant, Forensic Response Section in Saipol.
  • 21 years as a police officer, 10 years in crime scene investigation.
  • Overview of role in Forensic Response, focusing on ballistics.

Overview of Forensic Ballistics

  • Two main areas:
    • Laboratory work: Classifying firearms for court.
      • Determining firearm classifications according to the Firearms Act of South Australia.
      • Analyzing ammunition to confirm its nature and suitability for submitted firearms.
    • Scene work: Investigating shootings.
      • Police shootings, homicides, suicides, drive-by shootings.
      • Trajectory analysis to determine shooter's location.

Ammunition Examination

  • Key aspects:
    • Caliber identification.
    • Bullet composition.
    • Case materials.
    • Primer types.
    • Head stamps for identification.
    • Wildcat cartridges.
    • Identification of reloaded ammunition.

Ammunition Components

  • Components:
    • Case.
    • Primer.
    • Propellant.
    • Bullet.
  • Types:
    • Centerfire.
    • Rimfire.
    • Shotshell.

Breakdown of Ammunition Types

  • Centerfire: Primer in the center of the cartridge.
  • Rimfire: Primer around the outside base of the cartridge.
  • Shotshell: Center primer; contains multiple projectiles.

Detailed Ammunition Components

  • Cartridge case: Holds all components.
    • Materials: Aluminum, plastic, brass, coated steel (armor-piercing).
  • Primers: Rimfire or centerfire.
  • Bullets: Various sizes and shapes.
    • Materials: Plain lead or jacketed with copper/brass.
  • Propellant: Burns when ignited by the primer.
    • Types: Slow, fast, or neutral burning.
  • Shotgun ammunition: Contains multiple projectiles within the case.

Caliber Explained

  • Definition: Term describing the firearm's chamber discharge, related to the bore of the firearm barrel.
  • Measurement: Expressed in fractions of an inch or millimeters.
    • Inch: e.g., .22.22 caliber.
    • Millimeters: e.g., 9 mm×19 mm9 \,\text{mm} \times 19 \,\text{mm}.

Ammunition Naming Conventions

  • No strict rules for naming.
  • Names can refer to:
    • Bullet diameter.
    • Manufacturer.
    • Year of production.
    • Cartridge case length.
    • Propellant grain amount.

Examples of Caliber Names

  • 9 mm9 \,\text{mm} Parabellum: Bullet diameter (9 mm9 \,\text{mm}) + manufacturer (Parabellum).
  • 7.62×39 mm7.62 \times 39 \,\text{mm}: Military term.
  • .30−06.30-06 Springfield: Caliber (.30.30) + year produced (19061906) + location (Springfield).
  • 9 mm9 \,\text{mm} Parabellum can also be known as 9 mm9 \,\text{mm} Luger or 9 mm×19 mm9 \,\text{mm} \times 19 \,\text{mm}.

Shotgun Gauges

  • Based on weight division, not length.
  • Common: 12 gauge.
  • Refers to the number of lead pellets (sized to fit the bore) that equal one pound of lead.

Ammunition Identification

  • Head stamps: Indicate ammunition type and manufacturer.
  • Measurements: Case diameter, length, shoulder, neck, rim, etc.
  • SAMI (Sporting Arms and Ammunition Manufacturers' Institute) standards: Manufacturing standards available online.

Examples of Head Stamps

  • Rimfire: Winchester (X, H), Remington, CCI (C).
    • Same manufacturer may use different head stamps based on manufacturing location and year.
  • Centerfire: 6.5 /356.5 \,/ 35 PMC, 3838 Special Winchester, .40.40 Smith & Wesson Federal, year of manufacture (e.g., 19431943).
  • Shotshell: Gauge (e.g., 20) with manufacturer marks (stars).

Wildcat Cartridges

  • Definition: Handmade or invented cartridges by amateur firearms enthusiasts.
  • Purpose: To meet specific needs not available commercially.
  • Process: Modifying commercially made cases, changing barrels and chambers.
  • Commercialization: Some become popular and are commercially manufactured.

Importance of Wildcat Cartridge Knowledge

  • Stem from commercially made ammunition.
  • Head stamp may be misleading (e.g., .223.223 Remington).
  • Example: 300300 AAC Blackout, developed for military use in Afghanistan and now commercially available.

Reloading Ammunition

  • Process: Replacing primer, propellant, and bullet in a fired case (mainly centerfire and shotgun).
  • Reasons: Perceived cost reduction.
  • Examiner awareness: Reloading standards may vary from SAMI standards.

Firearm Knowledge

  • Types of firearms.
  • Different actions.
  • Barreling manufacturing and rifling techniques.
  • Rendering firearms safe.
  • Disassembly and reassembly.
  • Manufacturer's marks and proof marks.
  • Safety mechanisms.
  • Improved and modified firearms.
  • Serial number restoration.
  • Suppressor examination.

Reasons for Firearm Examination

  • Firearms Act of South Australia 2015: Categorization (A, B, C, D, F).
  • Safety mechanism functionality reporting.
  • Test firing for national database.
    • Matching firearms to scenes and potentially to individuals.
  • Reporting for court or criminal matters.

Types of Firearms

  • Rifles.
  • Handguns.
  • Shotguns.
  • Homemade or modified firearms.
  • Black powder (antique firearms).

Homemade Firearms

  • Often constructed from hardware store materials (e.g., PVC piping).
  • Vary in sophistication and functionality.
  • Attempts to convert blank firing firearms into live firing firearms.

Examples of Firearm Conversions

  • Blank firing handgun: Attempted conversion with a drill bit left in the barrel.
  • Blank firing revolver: Fully converted to live fire by replacing the hammer and barrel, and drilling out obstructions.
  • Torch firearm: Disguised as an ordinary torch.
  • Pen gun: Disguised as a metal pen, capable of firing a .22.22 long rifle caliber bullet.

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: Automatic loading and unloading with each trigger pull.
  • Pump action shotguns and rifles: Manual slide action to load and unload. Can have exposed or internal hammers.

Handguns

  • Self-loading pistols: Popular among outlaw motorcycle gangs (e.g., Glock).
    • Automatic loading and unloading with each trigger pull.
    • Vary in sizes, shapes, and calibers.
    • Exposed and internal hammers.
  • Revolvers: Single and double action.
    • Single action: Manual cocking of the hammer.
    • Double action: Trigger pull cocks and fires the gun.

Shotguns

  • Break action: Manual opening for loading.
  • Pump action: Tubular magazine, manual slide action.
  • Self-loading: Automatic loading, capacity of about five rounds.

Self-Loading Rifles

  • Colt AR-15: Common in mass shootings.
    • Rapid firing of .223.223 Remington bullets.
  • Caliber differences: .223.223 vs. 5.56 mm5.56 \,\text{mm}.
    • Interchangeable, but 5.56 mm5.56 \,\text{mm} may cause more wear on a .223.223 firearm.

Parts of Firearms

  • Rifle: Barrel, forestock, magazine, trigger, butt, shoulder stock, bolt.
  • Revolver: Barrel, frame, grip, trigger, cylinder, hammer.
  • Self-loading pistol: Slide, magazine, extractor, ejector.

Mechanics of Self-Loading Pistols

  • Slide action: Recoil causes the slide to move backward, ejecting the spent cartridge.
  • Magazine spring: Pushes rounds up into the chamber.
  • Extractor and ejector: Located inside the frame and slide, used to unload the spent cartridge case.
  • Striker action: Hammer hits the striker, which hits the firing pin, igniting the primer and propellant.
  • Gas propulsion: Gases propel the bullet out of the cartridge case and down the barrel.

Gunshot Residue (GSR)

  • Composition: Lead, barium, and antimony.
  • Source: Propellant, lubricant, primer.
  • Soot: Carbonous material from burning gas.
  • Collection: Sticky stubs to collect particles from hands or clothing.
  • Time limit: About 4 hours for effective collection.
  • Factors affecting collection: Washing hands, putting hands in pockets.

Shotgun Discharge

  • Large amount of propellant.
  • Wad: Holds projectiles together.
  • Projectile Dispersion: Projectiles spread with distance.

Internal Mechanisms of Firearm Barrels

  • Rifles and handguns: Rifled barrels with grooves and lands.
  • Shotguns: Smooth bores. No rifling is needed because the water encases them as they leave the barrel.
  • Rifling: Grooves cut into the barrel create a spin on the bullet for stability, distance, and accuracy. Greater Accuracy.

Rifling and Bullet Identification

  • Rifling process: Leaves unique striae (marks) on the bullet, acting as a fingerprint.
  • Comparison microscopy: Used to match bullets to specific firearms.

Scene Investigation

  • Scope: Ballistics, shoe mark impressions, blood pattern analysis (BPA).
  • Evidence collection: Spent cartridge cases, spent projectiles, shotgun wads.

Comparison Microscopy

  • Cartridge cases: Breech face marks (e.g., rectangular marks from Glocks), firing pin impressions.
  • Individual marks (striae): Unique to each firearm due to manufacturing imperfections.
  • Class characteristics: Marks common to certain types of firearms.
  • Firing pin impressions: Unique indentations on the cartridge caused by imperfections or damages from the firing pin.
  • Rimfire cartridges: Individual striae marks on either side of the car cartridge.
  • Bullets:
    • Rifling: Striae marks left on bullets as they pass through the barrel.
    • Comparison: Matching striations on test-fired bullets with those found at crime scenes.