Forensic Firearms Identification
| Published date | 01 October 1939 |
| DOI | 10.1177/0032258X3901200409 |
| Date | 01 October 1939 |
| Author | J. Edgar Hoover |
| Subject Matter | Article |
Forensic Firearms Identification"
By J.
EDGAR
HOOVER,
Director, Federal Bureau of Investigation, Washington,
U.S.A.
FORENSIC
firearms identification involves the scientific
examination of evidence resulting from the use of firearms.
This
evidence usually consists of the weapon itself, the fired
projectile or the cartridge case.
In
addition to the examination
which seeks to determine the weapon in which the projectile
or cartridge case was fired, it is part of the expert's work to
prepare photomicrographs for the purpose of substantiating
his opinion and demonstrating the same in court.
MARKINGS
The
identification of firearms evidence is predicted on the
principle that the softer metals used in the manufacture of
bullets and cartridge shells are indelibly imprinted with the
metal patterns of the hard steel surface of the firearms with
which they come in contact.
In
the manufacture of a rifled
arm, lands and grooves are cut into the interior surface of the
barrel for the purpose of twisting the bullet into a spin as it
progresses through the gun.
The
ballistic significance of this
twist on the bullet is to cause it to hold straight and true in its
course after it leaves the muzzle of the weapon.
In
cutting
these lands and grooves the hard steel surface of the barrel is
left, even after final polishing, with microscopic imperfections
caused by the cutting tools. Subsequent use and wear also
contribute to this pattern of imperfections.
The
fired bullet is
generally
cut
by the lands as it passes through the barrel in
such a manner that an examination of this bullet surface will
readily indicate the width of the lands and grooves and the
direction of and degree of pitch to the twist.
This
information
in itself frequently permits firearms identification experts to
determine the model of the gun from which the bullet was
•
Reprinted
with
the
permission of the
Author
and of
Dr.
F. C. Warnshuis,
editor of the American
Joumal
of Medical Jurisprudence, in which publication this
article originally appeared.
445
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