Forensics Chapter 8

breechface marks

when a cartridge is fired, the explosion forces the bullet down the barrel, the shell casing is forced back against the breech leaving impressions unique to the individual gun’s breech on the shell casing

Firing pin impression

(individual) a firing pin strikes the center ring of the cartridge leaving a distinct impression that is unique to the firing pin of that gun

ejector and extractor marks

the extracting pin and ejector throw the spent shell casing from the chamber of the gun, these leave marks on the shell casing that are unique to those parts on that firearm

what is the reagent used in the modified gries test?

Diphenylamine

what chemical does the reagent react with to produce a positive result in the modified gries test?

nitrates

what part of the cartridge is the nitrates found?

In the primer

what color is a positive modified greis test?

blue

What is the reagent used in the Sodium Rhodizonate test?

Sodium Rhodizonate

What chemical does the reagent react with to produce a positive result in a sodium rhodizonate test?

lead

What part of the cartridge is the lead found in the sodium rhodizonate test?

The bullet or projectile

What color is a positive sodium rhodizonate test?

pink

What instrument is used in the SEM test?

Scanning Electron Microscope

What three elements must be present in a SEM spectrum for the sample to test positive?

Pb- Lead, SB- Antimony, and Ba- Barium

What part of the cartridge are Lead, Antimony, and Barium found?

in the primer

Besides identification of elements, what else can be learned by analyzing the SEM test?

It can provide information about the morphology and distribution of particles on the sample surface.

class characteristics of a cartridge

manufacturer, winchester, shape, rimless or rimmed, caliber, composition