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.