cartridge case impression evidence Flashcards
1
Q
cartridge cases
A
- unique tool marks impressed on to them by the action of loading and/or firing the weapon.
- can be striated (like the striae on bullets) which are produced by lateral movement of the cartridge case against the firearm or impressed when the firearm impacts the cartridge case with sufficient force to leave an impression.
- Like bullet ID, cartridge case examination is done through comparison with test fired examples except for things like headstamps which can be compared to databases.
2
Q
impression evidence may then come from:
A
- Deliberate marks left by the manufacturer (headstamps)
- The action of the weapon in general and/or loading
- The chamber
- The breech face–
- Shear marks (produced by drag of the cartridge case against the firing pin/breech face)
- The extraction mechanism (extractor claw and/or ejector)
- The extraction port
3
Q
cartridge case movement in the barrel (A)
A
- When a cartridge case is forced backwards from recoil the primer imbeds itself in the firing pin hole. -As the slide of the pistol starts to recoil, the barrel will drop slightly as the action opens.
- The dropping barrel forces the cartridge case to move down slightly and when this happens the lower edge of the imbedded primer is sheared downward and out of the firing pin hole.
4
Q
firing pin drag (B)
A
- In a similar process, striated marks calledfiring pin drag markscan be produced.
- When the firing pin springs forward to strike the primer of a cartridge, it may remain slightly forward and imbedded in the primer.
- Certain barrels (like in the GLOCK) drop down slightly as recoil is forcing the action open.
- The cartridge case drops with the barrel causing the nose of the protruding firing pin to drag across the primer as it leaves the firing pin impression.
5
Q
extractor and enjector marks
A
may or may not leave striated marks
6
Q
breech face marks
A
can take many different forms
