Firearms, Toolmarks

types of bullets

shot gun shells

rifiling and rifled barrels

-lands (raised) and grooves (cut) on the inside of metal tube

-imparts stability on bullet

broach rifling

all grooves are cut simultaneously w/ a series of progressively larger cutters

-tool changes microscopically between guns meaning each land and groove is unique

caliber

inside diameter of the bore measured from land to land

"rifled" weapons

-handguns

-semi-autos

-revolvers

-rifles

"non rifled" weapons

shotguns

markings on cartridge cases...

-firing pin impressions

-breech-face marks

-extractor and ejector marks

-marks from the magazine

firearm databases

-IBIS

-NIBIN

serial number restoration

chemical etching involves the removal of the outer layers of the metal to reveal the impressed characters underneath, strong acids are typically used to remove the metal

toolmark comparison technique

test markings are made with the tool in lead or other soft material

-compared under a comparison microscope

propellant residue

follows the bullet out of the barrel

-can be deposited on clothing of victim or other surface

-usually the result of gases + particles escaping

primer residue

from explosion of the primer

-microscopic particles expelled from a firearm during discharge

-composed of elements from the primer mixture of the ammunition

6-12 inches

how far does smoke travel?

propellant particles

the diameter of the spread of the particles increases as the muzzle distance increases

-usually only travel up to 3-4 feet

test firings

what can be used to get a better approximation of muzzle distance?

Griess Test

-chemical test for nitrites in GSR

-reacts with burned gun powder to produce and orange color

Sodium Rhodizonate Test

-tests for lead

-chemical reacts with lead and produces purple color

shotgun ammunition

pellets spread out as they exit the barrel

secondary transfer of GSR

depending on the surface, primer residue can be easily transferred to another surface

collection of primer residue

removed from the backs and palms of hands using adhesive lifts that are mounted on a stub

-right hand, left hand, and negative control

-elemental composition analyzed using SEM (typically antimony, barium, and lead)