CC triage

CC nomenclature

headstamp (manufacturer and caliber), primer, FPI, FP drag, FPAI, FPAI sheering, BF marks, extractor/ejector

Definition of Class Characteristics

Measurable features of an item that indicate a restricted group source.

Based on design factors determined prior to manufacture

May be shown to be like or consistent with a questioned source, although not uniquely identifiable with that source

Generally can be seen with limited magnification

What are the Class Characteristics NIBIN determines?

-caliber

-ejector location and shape

-extractor location and shape

-breech face finish

-firing pin aperture shape

-firing pin shape and finish

-metal injection molding (MIM) mark

Definition of Individual Characteristics

-Marks on an object produced by the random imperfections or irregularities on the surface of tools used to manufacture the object

-Produced incidental to the manufacturing process and typically seen at the microscopic level

-Can be a result of use, damage, or corrosion

-Unique to the tool that made the item

Function Marks

Cycling marks: ejector, extractor, ejection port

Firing marks: breech face, chamber, firing pin

What are breech face marks?

A negative impression of the breech face of the firearm found on the head of the cartridge case and/or primer after firing. It is caused by the pressures produced during firing.

Types of breech face marks?

Arch, circular, crosshatch, granular, parallel, smooth, combination

Primer manufacture marks

Pre-existing marks on the primer before firing that remain after firing.

Firing pin marks:

FPI: shape, finish

FPAI (flowback): shape (circle, teardrop, rectangular, oval), sheering

FP drag

What is a firing pin?

The part of a firearm mechanism which strikes the primer or rim of a cartridge to initiate ignition in order to fire a cartridge

What is the firing pin impression(FPI)?

the indentation of the primer of a centerfire CC or in the rim of a rimfire CC caused when it is struck by the FP

What is the FP drag mark?

The impression produced when a projecting FP comes in contact with a CC during the extraction/ejection cycle

What is FP aperture?

The hole in the breech face of a FA through which the FP protrudes

What is primer flow-back?

The extrusion of the primer into the firing pin aperture.

What is FP aperture shear?

Striated marks caused by the rough edges of the FPA scraping the primer metal during unlocking of the breech.

What are the FP shapes?

Rimfire: circle, rectangle, semi-circle, flat, hemispherical, rectangular: regular, square, angular; crescent

Centerfire: circular, circular (angular), hemispherical, hemispherical (D-shaped), elliptical, rectangular

FPI finishes?

Concentric circles, granular/smooth

What is the FPI Metal Injection Molding Mark?

A manufacturing process which involves combining fine metal powders with plastic binders which allow the metal to be injected into a mold using equipment similar to a standard plastic injection molding machine. Often used to make small, complex, metal parts. Looks like a single line running all the way through the FPI.

FPAI shapes:

rectangular, oval, circular, teardrop, undefined/none

Where is the FPAI shear?

On the left side of the FPI/FPAI