Unit 10: Ballistics and Explosives
10.1 Introduction and Classification of Firearms
Forensic ballistics — the firearms-and-ammunition science: the interior (the firing’s physics), the exterior (the projectile’s flight), the terminal (the impact’s effects) — and the forensic’s own: the comparison (the fired evidence’s matching). The classification (the exam’s core):
- By the bore: the smooth-bore (the shotguns — the pellets’ spread) vs the rifled (the pistols, revolvers, rifles — the spin’s accuracy).
- By the size-and-hand: the handguns (the pistols-semiautomatic; the revolvers-cylinder) vs the shoulder (the rifles; the shotguns; the carbines).
- By the action: the manual (the bolt, lever, break) vs the self-loading (the semi; the full-auto — the machine guns).
- By the calibre (the bore’s diameter — the mm-and-gauge’s measures).
10.2 Characteristics and Firing Mechanism of Firearms
The mechanism’s cycle (the exam’s sequence): the cartridge’s loading → the trigger’s pull → the firing pin’s strike → the primer’s ignition → the propellant’s burn → the bullet’s propulsion (the pressure) → the spin’s-and-flight (the rifling’s grip) → the extraction-ejection (the case’s ejection — the scene’s evidence). The firearm’s individuality: the rifling’s manufacturing marks (the lands-and-grooves’s number, twist-and-width — the class) + the bore’s-and-breaching’s irregularities (the wear-and-use’s marks — the individual) — the fired bullet’s signature.
10.3 Matching Crime and Testing Bullets and Cartridge Cases in Firearms
The comparison’s process: the test firing (the suspect gun’s evidence-bullets-and-cases produced under the lab’s controls); the comparison-microscope (the side-by-side — the bullets’-and-cases’ microscopic striae); the matching (the lands-and-grooves’s agreement — the consecutive-matching-striae criteria); the cartridge case’s marks (the firing pin’s impression, the breech face’s marks, the extractor-ejector’s traces — the gun’s signature on the case). The evidence’s collection: the bullets-and-cases at the scene (the location’s documentation — the trajectory’s input); the wounding’s recovery (the autopsy’s-and-surgery’s bullets). The conclusions’ discipline:
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