Forensics Exam II: Ch.9 - Firearms, tool marks, and other impressions

Handguns

Pistols and Revolvers

Pistols

1 round at a time, can be semi-auto

Semi-automatic Pistol

has a removeable mag and ejects spent cases

Revolvers

several firing cylinders (breaktop, swingout, or solid frame)

Long Guns

can be single shot, semi-automatic, or fully automatic

shot guns

has lands and grooves

Shotguns

uses balls/shots insteadof bullets, narrower barrel, can use rifled slugs for accuracy, diameter determined by gauge, higher guage = smaller diameter, gauge is pellets per pound

Rifling a Barrel

cutter, stamp, or mandrel

Broach Cutter

Cut the metal to make the grooves for the rifling

Stamp

Stamps in the grooves for the rifling

Mandrel

Used to hammer in the grooves for rifling

Class Characteristics of Bullets and Cases

diameter, color, manufacture

Individual Characteristic of Shell Cases

caliber, firing pin impression, breech marks, striation marks, ejector and extractor mechanism

DrugFire

FBI’s first ballistic search tool

IBIS

ATF’s first ballistic search tool

NIBIN

Currently used by FBI and ATF

Distance Determination

• Utilize gun powder and smoke distribution

• A star pattern indicates a close range shot

• A shot made from a distance greater than 18 inchers doesn’t leave much residue, just the hole

Greiss Test

tests for barium and antimony

Collecting and Preserving Firearm Evidence

hold weapon by edge and unload it, if it’s a revolver record it’s initial position

Restoring Serial Numbers

• Chemical Etching: acid or base with an oxidizing or reducing agent

• Electrochem etching: chem etching with an electrical current/voltage

Class Characteristics when Comparing Tool Marks, Footwear, and Tire Impressions

can help identify general brands and manufactuers

Individual Characteristics when Comparing Tool Marks, Footwear, and Tire Impressions

finding imperfections within these help create individuality

Casting of Impressions

dental stone for shoeprints and use spray wax for wet surfaces