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Examination of Firearms William Conrad “Module 08: Examination of…
Examination of Firearms
William Conrad “Module 08: Examination of Firearms.” Firearm Examiner Training, National Forensic Science Technology Center, projects.nfstc.org/firearms/module08/fir_m08.htm.
Cycle-of-Fire Steps
Obturation: powder gasses are sealed
Unlocking: cartridge is unlocked
Firing: pulling the trigger releases the firing pin
Extraction: loosens cartridge case from chamber
Locking: cartridge is locked into place
Ejection: cartridge case is flipped out of chamber
Chambering: also putting a cartridge in the chamber
Cocking: bolt is retracted
Feeding: putting cartridges in the chamber
manual or automatic
Handguns: revolvers vs. pistols
Autoloading: semiautomatic pistols
Have to pull the trigger for each shot, but the energy from shooting is harnessed to fuel extraction, ejection, cocking, and loading
Blowback, recoil, and gas-operated action
Autoloading: full automatic pistols: only have to pull the trigger once to perform the firing cycle over and over
Double-action revolvers: similar to single-action, except the hammer is cocked and released in one motion, and ejection and extraction is slightly different
Single-and multibarreled pistols
Trigger systems: single action, double action, and double action only
Single-action revolvers: single chain of events leads to firing of firearm
Firearms Identification Information
Military Firearms
Symbols and codes to show manufacturer
Don't have caliber designation
Must measure bore diameter and chamber and know common military ammunition to determine caliber
Proof Marks: can help identify a firearm when the manufacturer is not present on firearm
Things to record: brand, serial number, model, caliber, and importer
must differentiate between caliber and manufacturer
Examination: perform preliminary examination and then get more specific
Trigger pull: trigger weights, spring scale, digital scale
Safety features: be careful where you point firearm, keep finger off trigger, keep unloaded
Long guns: determine magazine capacity, cycle action, determine automatic capabilities, selector switch, cock firearm, pull trigger, cycle action, detect choke, test trigger pull and safety functions, and test fire
Test firing: document function, bullet recovery, and additional testing
Single and multi barreled pistols: determine action capacity, test trigger pull and safety functions, and test fire
Drop testing
Autoloading pistols: find magazine capacity, cycle action, test trigger pull and safety functions, and test fire
Shock test
Revolvers: inspect cylinder for damage, test trigger pull and safety functions, and test fire
Long or Shoulder Firearms
Rifles
Magazines: removable box, internal box, rotary, tubular
Visual Examination: determine action type, magazine, caliber, telescopic sights, and safety
Action types: bolt, pump, autoloading, lever, falling block, rolling block
Shotguns
Single barrel action types: break open, pump, bolt, and semiautomatic
Choke controls spread of pellets- can be full, modified, or cylinder
Single and double barrels
Evidence Receipt
Document receipt of evidence and make sure firearm is on safety
Examination Documentation
Should be thorough and consistent with laboratory protocol
Any research used during examination and documentation should be added to case file
Check if fingerprints or biological testing needs to happen before beginning examination