Basics - Firearms and Ballistics Notes

Caliber and Chambering

  • Caliber: Projectile diameter.
  • Chambering: Cartridge length.
  • Example calibers: 7.62 x 39 mm (Russian AK47), 7.62 x 51 mm (NATO), 7.62 x 54 mmR (Russian), 7.62 x 25 mm (Tokarev).
  • Three systems of measurement:
    • Metric (e.g., 5.56 mm)
    • Imperial (e.g., 0.223")
    • Caliber (e.g., 223 cal)

Ammunition Safety

  • Using the wrong sized round can cause firearm damage or failure.
  • Undersized rounds can rupture, causing a shock front and potential breech failure.

Headstamp

  • Maker's mark on the base of the cartridge.
  • Can indicate the end-user (e.g., "MOD" for UK military).

Cartridge Case Investigation

  • Identify manufacturer and design via headstamp examination.
  • Determine mechanisms/use from size, shape, and physical features.

Self-Loading vs. Single-Shot

  • Self-loading firearms use cartridges without protruding base rims and parallel sides for magazine stacking.
  • Single-shot mechanisms (e.g., revolvers) use cartridges with protruding base rims.

Cartridge Case Measurement

  • Use a micrometer or digital Vernier calliper for accurate measurements.
  • Dimensions include caliber and chambering lengths (e.g., 5.56 x 45 mm and 5.56 x 49 mm).

Class Characteristics

  • General dimensions
  • Caliber and chambering
  • Shape of firing pin mark
  • Primer type
  • Headstamp information

Typical Cartridge Marks (Individual Characteristics)

  • Slide drag mark
  • Slide scuff mark
  • Firing pin scrape mark
  • Firing Pin Impression
  • Ejector mark
  • Breech face marks
  • Extractor marks
  • Magazine lip marks
  • Chamber marks
  • Ejection port dent

Shotgun Ammunition

  • Headstamp present; body often plastic or card with a metallic head.
  • Manufacturer data may be printed on the cartridge body, but headstamp is more reliable.

Bullet Basics

  • Projectile below 20 mm fired from a barrelled weapon.
  • Typically has a lead core.

Bullet Composition

  • Lead antimony alloy core (e.g., 97% Lead, 3% Antimony).
  • Jacketing protects the lead core.

Jacketing Purpose

  • Prevents rifling drag at higher velocities.
  • Improves rifling pick up and reduces deformation.

Bullet Types

  • Unjacketed: Lead alloy only, low velocity, high deformation.
  • Semi-jacketed: Soft point (SP), hollow point (HP), polymer tipped (PT); less deformation, low penetration.
  • Fully-jacketed: Full metal jacket (FMJ); excellent penetration, high stability.

Bullet Statistics

  • Smallest caliber: 4.3 mm.
  • Typical velocities:
    • Handgun: 200 - 400 \frac{m}{s}
    • Rifle: 300 - 1500 \frac{m}{s}
  • Acceleration: A rifle bullet can undergo around 150,000g when fired.

Bullet Recovery

  • Handle with care to avoid further marking.
  • Recover the whole impacted item if embedded.

Ideal Shooting Investigation

  • Suspect firearm (with serial numbers).
  • Ammunition components from the scene.
  • Ammunition for test firings.
  • Use firearm-related data and additional evidence (DNA, fingermarks) to build intelligence.

Test Firings

  • Soft capture bullets using water tanks, rubber tyre pieces, or specialist fibre boxes.

Forensic Ballistic Technologies

  • Comparison microscopy (older technology, requires expert verification).
  • IBIS (Integrated Ballistics Identification System): Current leading process using high-definition imaging and 3D scanning.

NABIS (National Ballistics Intelligence Service)

  • UK's firearms intelligence service with a national IT system.
  • Tracks ballistic items from recovery to destruction.
  • Links incidents to people, crime groups, and events.

Items to Record on NABIS

  • All firearms in police possession.
  • Licensed firearms used in crime.
  • Firearms and imitation firearms used in crime.
  • Ammunition subject to control.
  • Licensed firearms reported lost or stolen.
  • Surrendered firearms matching NABIS criteria.
  • Electronic stun guns.

Summary

  • Understand terminology and apply it to ammunition.
  • Familiarize with common caliber and chambering types.
  • Understand how marks are made to know where to look.
  • Bullet class characteristics:
    • Caliber
    • Construction
    • Land mark width
    • Groove mark width
    • Rifling mark direction
    • Described angle
    • Twist rate
  • Understand how information is used in intelligence processes.