Firearm and Toolmark Identification: Part 2 Flashcards
Extractor marks causes contact with what parts of the firearm?
Extractor Mark (gouge) caused by contact with the extractor-
[1] as the cartridge rises up from the magazine and behind
the extractor then seats in the chamber, or-
[2] as the extractor snaps into the extraction groove after
riding over the rim.
Types of Chamber Marks
- Banded Strise
- Banded Spiral
- Fluting
- Ramp Bulging
- Diagonal
- Rust
What are the four (4) steps in the examination process?
- Level 1 analysis: Class Characteristics
- elimination, but not individualization can occur
here - Level 2 analysis: Comparison Microscopy
- Individualization can occur here
- Level 3 analysis: Conclusions Drawn
- Identification, Elimination, Inconclusive
- Level 4 analysis: Confirmation of Identifications
What are the class characteristics of cartridge cases?
- Calibre (cartridge designation)
- Types of breech marks
- Shape of firing pin impression
- Drag and sheer mark
What are individual characteristics in toolmark examination
Marks produced by random imperfections or irregularities of tool surfaces. They are unique to that tool to the practical exclusion of all other tools.
What is a way in which individual charcateristics can be made?
These random imperfections are produced incidental to manufacture and/or caused by use, corrosion or damage.
What is flowback?
Flowback is the extrusion of the primer into the firing pin hole.
What causes flowback?
Flowback is as a result of the primer inertia which is caused by the
slide of the firearm rapidly moving rearward then suddenly
coming to a halt.
What are subclass characteristics?
Features produced during manufacture that are
consistent among items fabricated by the same tool
in the same approximate state of wear.
Are subclass characteristics determined before or after the manufacturing process?
These
features are not determined prior to manufacture
and are more restrictive than class characteristics.
What is the relationship between the surface of the cartridge case and the toolmarks on the inside of the chamber, and how does this relationship affect the potential for subclass markings?
The reaming process repeatedly cuts over toolmarks it creates, eliminating the potential for subclass. additionally, because the surface of the cartridge case moves perpendicular to the toolmarks on the inside of the chamber this further means there is no potential for subclasss.
What is a broach?
A Broach is a tool with a series of cutting edges of slightly increasing height which is used to remove a small layer of metal with each successive tooth in one pass of the tool.
What is the purpose of broaching?
Broaching is used to machine round, contoured and flat
Surfaces such as breach faces
When is subclass potential is high?
If toolmarks extend for the length of the bore the subclass potential is high.
When should rifling be further inspected?
If rifling marks are parallel with the rifling then further inspection for subclass should be done.
Explain the importance of examining firearm components for like discontinuous lines?
The examiner should exercise caution and look for discontinuous lines, defects in the surface and marks indicative of breakage or chip formation.
What is the appearance of breechface marks?
- Straight, parallel broached/milled.
- Subclass would appear as straight/continuous
- Impressed by bolt face
During the breechface examination what should one look for?
Look for marks that are nin-ctinuous compare one end with anothe for better clarity.
What do straight but irregular breechface marks suggest?
Filing/Ground
What kind of subclass potential does filing/ground have and why?
Minimal subclass potential’ marks are not continuous and combination of coarse an fine tool marks.
How is miling achieved?
Milling is achieved by gradually removing metal from the
Breechface by using rotating toothed cutters.
What affect does milling have on the breechface?
Milling of breechfaces can result in concentric rings or arcs on the surface of the breechface.
What kind of subclass potential does milling have?
Similar to broaching, miling has discontinous lines in which examiners should exercise caution about.
What is grinding?
Grinding of breechface removing metal in the from of small chips.
