Physical Methods - Firearms

Rimfire

Firing pin crushes rim

Centerfire

Firing pin strikes center of primer

Lands

Raised parts inside metal tube

Grooves

Cut parts inside metal tube

Caliber

Measurement of diameter from land to land. Measured in hundredths of an inch, or millimeters

“Rifled” Weapons

Handguns (semi-automatic, revolvers), rifles

“Non-rifled” Weapons

Shotguns

Markings on Cartridge Cases

Firing pin impressions, Breech-face marks, Extractor marks, Ejector marks, Marks from the magazine

NIBIN

National Integrated Ballistics Information Network

IBIS

Integrated Ballistics Identification System

Toolmark Comparison

Test markings are made with the tool in soft material. The markings are compared under a comparison microscope

Propellant Residue

From front of gun. Deposited on clothing of victim or other surface. Primarily consists of residue left in the barrel and from material inside the cartridge case.

Propellant Particles

The diameter of the spread of particles increases as muzzle distance increases. Usually travel up to 3 - 4 feet.

Griess Test for Nitrates

Reacts with burned gunpowder to produce an orange color

Sodium Rhodizonate test for Leads

Chemical that reacts with lead to produce a purple color

Primer Residue

Residue from the back of the gun

Primer residue typically consists of:

Antimony, barium, and lead

Timeframe to collect primer residue:

Approximately four hours. Easily lost from normal activity

Removal of primer residue

Removed from palms and backs of hand using 3 stubs (Right hand, left hand, control)

If a negative control appears possible:

Analysis results are negated

If alternative materials are found:

Particle is generally not considered to be characteristic of primer residue