Helston Forensics

Forensic Ballistic Laboratories at Helston Factory

Forensic Question Of The Month -Forensic Strategy

When preparing a forensic strategy note EVERYTHING that needs to be considered before preparing your action plan, this is particularly important when examining a single exhibit… some actions have irreversible consequences, for instance: do you fire your only round of ammunition?

Scenario

Cartridge case and fired bullet found at the scene, the exhibits have arrived at the firearms lab with the instructions:

1. What information can be obtained from the exhibits?

2. What markings / information can be obtained that can be compared with future findings?

Bearing in mind the forensic strategy gives us all the idea’s that help us form the examination plan, EVERYTHING must be considered. ( Note: The bullet and case on cursory examination look like they were fired from a 9mm Glock pistol.)

Some suggested headings: Information obtainable from the cartridge case; Information obtainable from the fired bullet; Information obtainable from the GSR; Tests to identify markings that could be replicated; Identification of cartridge case; Identification of bullet.

This is not a test of skills; it is an example of things that may not have been considered, to be shared by everyone. Don’t be afraid to chip in; your replies will always be posted anonymously and of course, you can e-mail us using your ‘handle’ (which can be funny but not rude!)

Full Boar

“Consider the following for the case: ejector mark, extractor mark, firing pin mark. And for the bullet: rifling marks. That’s all I can think of.”

Roy Rogers

Cartridge Case:

Feed into magazine (hand), Feed into magazine (loader), Round under fed round marked by round, Mark of under round by mag tube, rounds as they move down the tube marked by mag tube, top round marked as mag is put into pistol (contact with feed horn), case and rim of head marked by feed horn when the slide is drawn back, mark as front of feed horn contacts head of cartridge, mark on case by lips of mag as case moves into chamber, mark of under cartridge pushing up against case being stripped, mark as case is freed from mag lips and makes contact with under-side of breech face, mark on inside of case rim made by ejector, mark as case feeds into mouth of chamber, mark on front of case as it is stopped by front of chamber, mark made by extractor if slide is closed on chambered round, types of mark made by 3 different extractor types, extra pressure effect of incorrect spring loaded bearing, firing pin mark in primer on firing/multiple hit?, mark of primer around firing pin radius, mark from 2 sides of breech face on primer, mark on head of case made by breech face, effect of pressure on breech face markings, effect of pressure on firing pin markings, effects of pressure on primer flattening, effect of pressure on head of cartridge flattening, mark of extractor slot in slide, mark of ejector slot in slide, mark of feed horn on round in magazine (hi speed), mark of ejector/ multiple marks, mark of extractor on inside of case rim, tornado mark (case hitting ejection port edge), case sizing die impressions, case hardness profile, primer pocket machining marks, GSR deposits in case, head stamp impressions, rim profile, different pressure with mag loaded with 1 to 17 rounds, markings if round is loaded into chamber by hand slide released from hold open position. If slide is let forward slowly, mark of cartridge loaded on top of cartridge in magazine (1 cartridge to another), primer seal type/damage, case stretch (C.H.S), case diameter, deposits on outside of case (blood, fibres, paint etc.), DNA/fingerprints, reloaded?, resized?

Bullet:

Total evidence? (blood/fibres etc.), mark of round fed into magazine over a round already in magazine, mark of feed horn as slide is drawn to rear, mark from feed ramp, mark of mouth of chamber, skid mark of commencement of rifling, rifling impressions, base of bullet compound deposits, trace evidence from impact (blood, fibre, skin, hair, paint, glass etc.)

Consider:

Manufacture comparisons of case/propellant/primer components, same factory, same batch (components), correct combination (bullet/case/propellant).

Pistol components and method of testing:

Correct combination of marks? Firing pin/extractor/ejector/tornado/etc. Method of testing: 1. Load one round in mag, place mag in gun, rack and fire. 2. Fire by hand or by remote? (Ransom etc.) 3. Load full mag and note the difference between marks due to magazine spring pressure. 4. Tight grip/ loose grip effect.

Pre-read all AFTE articles Re: Glock

Other things to consider: Ammo batch, chronograph readings, ammo type, photography (hi speed), microscopy (colour or black and white), does GSR match typical compositions expected.

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