Week 2 - Forensic Ballistics Revision Study Notes

Overview of Forensic Ballistics

• Definition: Forensic ballistics is a branch of forensic science focusing on the analysis of firearms and ammunition in criminal investigations; it examines the phenomena related to projectiles and the forces acting on them.

Contents

1. What is Forensic Ballistics?

2. Sub-divisions or Classifications of Forensic Ballistics

3. Usefulness and Application of Forensic Ballistics

4. Firearms Classification

5. Classification of Firearms and Ammunitions

What is Forensic Ballistics?

• Forensic ballistics combines multiple scientific disciplines to analyze firearm-related evidence from crime scenes.

  • It includes the study of bullets, cartridge cases, and the mechanisms that fire weapons, as well as their impact on target areas.

Sub-divisions or Classifications of Forensic Ballistics

• There are four major divisions of forensic ballistics:

  1. Internal Ballistics: Studies the processes from the ignition of the propellant up to the projectile's ejection from the firearm.

  2. External Ballistics: Analyzes the flight of the projectile through the air until it impacts a target.

  3. Intermediate Ballistics: Integrates concepts from both internal and external ballistics to provide a comprehensive analysis of projectile behavior.

  4. Terminal Ballistics (also known as Wound Ballistics): Focuses on the effects and interactions of the projectile on the target at the moment of impact.

Usefulness and Application of Forensic Ballistics

• Forensic ballistics has multiple applications, including:

  1. Protection, Defense, or Resistance: Understanding firearms for personal protection and defense strategies.

  2. Investigation of Crime: Analyzing gunshot evidence to solve crimes and gather information in criminal investigations.

  3. War/Armed Conflicts: Assessing ballistic evidence in military contexts to evaluate weapon effectiveness and impacts.

  4. Legality, Acquisition, Possession, and Trade: Understanding laws surrounding firearms to ensure compliance and safety in possession.

  5. Engineering and Reconstruction: Assisting in recreating crime scenes through ballistic evidence analysis to understand events.

Classification of Firearms

• Difference between Guns and Firearms: UK law defines a firearm as any lethal barrelled weapon meeting specific criteria:

  • A lethal barrelled weapon: A weapon that can fire a shot, bullet, or missile with more than 1 joule of kinetic energy at the muzzle.

  • A prohibited weapon: Defined in Section 5 of the Firearms Act 1968; this includes specific banned weapons and ammunition.

• Classification of Firearms: Firearms can be classified into various types based on their design and mechanism:

  1. Handguns: Firearms designed to be operated with one hand; examples include pistols, derringers, and revolvers.

  2. Rifles: Firearms with a rifled barrel requiring shoulder support.

  3. Shotguns: Firearms featuring a smooth-bored barrel, also requiring shoulder support.

  4. Submachine Guns: Fully automatic firearms designed to fire pistol ammunition.

  5. Machine Guns: Fully automatic firearms designed to fire rifle ammunition.

Types of Firearms

• Handguns:

  • Can be fired using one hand.

  • Different types include revolvers (5-7 chambers) and pistols (single shot, semiautomatic, full-auto).

• Rifles:

  • Firearms with rifled barrels; they may be single shot, lever action, bolt action, pump action, or auto-loading.

• Shotguns:

  • Have smooth-bore barrels; variants include single shot, over and under, double barrel, and auto-loading.

• Submachine Guns:

  • Automatic firearms using pistol ammunition; typically short-barreled and blowback-operated.

• Machine Guns:

  • Automatic firearms firing rifle ammunition; designed to be supported by shoulder or stand.

Ammunition Composition and Nomenclature

• Ammunition is typically composed of four major parts:

  1. Cartridge Case: Houses other components; made typically of brass in rifled weapons.

  2. Primer: Located at the base; explodes upon impact to ignite the propellant.

  3. Propellant: Burns to produce gas for projectile propulsion; can be black powder or smokeless powder (single base or double base).

  4. Projectile (Bullet): The component that exits the muzzle; can be made of lead or treated with a metal jacket.

Nomenclature Example

• The cartridge is denoted as:

  • $7.62 imes 39 ext{ mm}$ (nominal bullet case length).

  • Can also be described using imperial or metric units (e.g., .223 Remington, .308 Winchester).

Cartridge Case Types

• Based on their shape:

  • Straight (e.g., always for pistol ammo), Bottleneck (e.g., always for rifle ammo), and Tapered (obsolete).

• Based on the extractor flange and base:

  • Rimmed, semi-rimmed, rimless, belted, and rebated.

Primer Details

• Centered Fire: Centrally placed primer assembly.

• Rimfire: Primer placed in the rim of the cartridge case.

Propellant Types and Characteristics

• Propellant is crucial for generating pressure; different types serve various purposes. The morphology of propellant affects performance.

  • Grain size, shape, and quantity depend on ballistic requirements.

Bullet Composition and Characteristics

• Bullet material typically consists of lead alloyed with tin and/or antimony, often jacketed.

• Bullet shapes include:

  1. Roundnose

  2. Wadcutter

  3. Semi-wadcutter

  4. Hollowpoint

Marks from Firearms on Ammunition

• The firing mechanism leaves tool mark impressions such as:

  • Firing pin impressions

  • Breech face impressions

  • Extractor and ejector marks

Marks on Bullets from Rifling

• The rifling pattern (lands and grooves) engraves the bullet, matching the barrel characteristics.

  • Different types of rifling include square or polygonal.

  • Shotgun rifling (if present) might be short near the muzzle.

Assessment of Rifling Characteristics

• Certain parameters of rifling assessed include:

  • Twist direction (left or right)

  • Number of lands and grooves (usually between 1 and 24)

  • Width of lands and grooves

Conclusion

• Forensic ballistics involves extensive examination of firearm and ammunition characteristics and their effects on criminal investigations. Understanding the detailed field of forensic ballistics can be pivotal in crime-solving and legal contexts.

Contact Information

• For further inquiries, contact Tolu Abejide at t.abejide@derby.ac.uk.