forensics midterm firearms

can be 2D or 3D deposition of a substance onto a substrate

removal of a substance from the receiving surface e.g. powder or dust

size and brand

unique wear patterns, cuts, foreign objects inbeded in tread

• photography
• casting (for 3D impression)
• gelatin lifer ( 2-D impression)
• electrostatic dust lifter -uses static 2Dd impressions
• collect item with print impression (shirt)

• use tripod
• make sure camera lens is perendicular to the impression
• take shot without scale then with a scale and identifier
• make sure impression fills entire frame
• use OBLIQUE lighting with flashlight or flash
• lighting less then 45% to print
• 4 different shots even in daylight

• finger print ink method -Rolled on paper
• vaseline method -vaseline on tred and rolled on paper process with black fingerprint powder
• specific to shoes
• collect
• biofoam

chemical enhancement used for impession in blood

bullet, caliber, general rifling, casing, caliber, brand, shape of firing pin mark

bullets, minute random/marking/straitions, casings, impressed marks/striated marks, due to structural irregularites/ variations

types of firearms

types of handguns 3

types of long guns

the diameter of the bore of a rifled firearm expressed in hundreds of an inch or mm .22 caliber, 9mm, .30 caliber, 7.62mm, .357 caliber

hollowed out by drilling during manufactoring cause microscopic drill marks that are random and irregular also impressed the inner surface with spiral grooves

spiral grooves that impart spin to the projectile when it is fired (so the bullet will go straight)

does a shot gun have rifling?

minute imprerfections on the rifling culters surface minute chips of steel pushed through random distribution and irregularites are impossible to duplicate to any two barrels even when manufactured in succession

• breechblock
• firing pin
• extractor
• ejector

• ammunition is propelled by the expanding gases created by ignition of smokeless powder of nitrcellube in cartridge
• unburned and partically burned particles of gunpowder plus smoke are propelled out

strippling, tattooing

soot, fouling

gun powder residue permits...the asessement of the distance from which a weapon was fired

smoke like vaporous lead surrounds entrance hole: fibers scorched stelle shape hole

halo of vaporous smoke, specks of unburned or partially burned powder grains observed up to 25"

no powder residue or powder grains bullet wipe around entrance hole

all 3 of these must be present in primer residue

any impression cut, gouge, or abrasion caused by a tool coming into contact with another object

size shape of mark

random nicks and breaks through use or random striations from manufacturing process

• swab for DNA
• photograph
• cast