Firearms and Toolmark Identification
The field of forensic sciences has experienced a recent surge of public interest, most of the principles the field was founded upon are not new.
This holds especially true for forensic firearms identification. Although firearms identification has made remarkable technological advances,
many of the same techniques and instruments which were first implemented over 50 years ago are still in use today.
The primary tool of every forensic firearms examiner, the comparison microscope,
has changed little since it was adopted in 1925. This instrument is justifiably considered the most significant contribution to the field,
since without it firearms identification would be impossible. The comparison microscope is actually composed of two individual microscopes
connected by an optical bridge. This allows the examiner to view two objects simultaneously with one-half of the field of view magnified by
one microscope while the other half is magnified by the second microscope. As a result of this development, identification of fired bullets
and cartridge cases became as conclusive as fingerprints.
Identification of fired ammunition to a specific firearm is made possible by distinguishing marks
the gun on the surface of both the bullet and the cartridge case. These markings fall into two categories:
class characteristics and individual characteristics. Class characteristics include general features such as the number of lands and
grooves and their width, direction of twist, and bullet diameter. Since many firearms are built to the same specifications, the variation
of these characteristics will be nominal from multiple guns of the same make and model. However, the individual characteristics imparted to a bullet
or cartridge case are different for every firearm, and make it possible for an examiner to positively identify
a round of fired ammunition as coming
from a specific gun.
Individual characteristics can be further classified into impressed or striated marks. Impressed marks are made by a hard surface imprinting its
shape into a softer material. These marks include those made by a hammer striking another piece of metal, or a screwdriver driven straight down onto
another surface. Striated marks are cause when a hard surface scrapes against a softer surface, such as pry marks made by a crowbar or when the surface
of the bullet is forced along the rifling inside a gun barrel. These marks can be present on cartridge cases, bullets, and other tools. Comparison
of the marks on the evidence with those on the test material can result in a "match", in which the striations on the two objects are synchronized and appear
to form a single image.
Firearm and Toolmark Services
Function tests (trigger pulls, etc.)
Comparisons to test bullets and evidence bullet
If the only evidence available is a bullet, the
bullet can be examined and a possible gun list
can be determined from the general rifling
characteristics on the bullet.
GRC analysis (general rifling characteristics)
Collection of red/brown stains (blood)
from items of evidence
Gunpowder residue analysis
Muzzle to target distance studies
Fracture match comparisons
Shooting scene reconstruction
Court testimony and presentations
For more information on Firearm and Toolmark Identification, please visit the