Mr. Cunningham. Of the breech face, it is approximately 17 times.
Mr. Eisenberg. There are a number of markings or lines on this breech face. Are these the microscopic characteristics which reproduce on the cartridge cases?
Mr. Cunningham. That is correct.
Mr. Eisenberg. And are the microscopic characteristics of this breech face individual to this weapon, to the exclusion of all other weapons?
Mr. Cunningham. They are.
Mr. Eisenberg. This is your method of determining that a given cartridge case has been fired from a given weapon?
Mr. Cunningham. The breech face marks, as well as the individual imperfections in the firing pin.
Representative Boggs. Let me ask a very elementary question, the answer to which I used to know years ago, but I have forgotten. Just exactly what does the firing pin do? What happens after that strikes?
Mr. Cunningham. Well, it is easier to start with the cartridge itself. The components of a cartridge are a bullet, a cartridge case, a primer in the base of the cartridge case, and powder.
Now, the primer is made out of a very soft metal that can be dented. These primers at manufacture are filled with, basically, an explosive. For instance, Remington-Peters cartridges have PETN, which is one of Du Pont's explosives. RDX is used as one of the components of Western cartridge cases, as well as lead styphnate, lead azides, and other explosive materials.