Transcript Firearms Identification

Firearms Identification
Forensic firearms examinations
identification of a bullet, cartridge case, or
other ammunition component as having
been fired by or in a particular firearm.
 the possibility for such singular
identification can be attributed to specific
machining processes used in the
manufacture of firearms.

Rifling
Helical grooves (rifling), cut into the bore
of a barrel of a firearm during production,
increase the accuracy of that firearm
 Effects:

Spin
 Stabilized
 Marks on the bullet (lands and grooves)

A rifled barrel:

will contain scratches, scrapes, and other
minute nicks and flaws
exacerbated through the subsequent use and
discharge of the firearm
 or as a result of natural wearing processes
such as rusting and corrosion


bullet will have unique microscopic
markings as a result
Firing pin impressions:

During the discharge of a firearm, the firing
pin strikes the primer of a cartridge,
creating microscopic contact marks and
unique indentations.
Breechface impressions:

As the powder within the cartridge begins
burning, the cartridge case is propelled
backwards against the breechface with
enough force to be impressed with the
characteristic microscopic features of that
surface.
When no firearm is recovered:



rifling parameters taken from the recovered
bullets can be used to determine the possible
manufacturers of the firearm from which the
bullets were fired.
General rifling characteristics or GRC are the
identified rifling pattern (i.e. 8/right) and the
diameters of the individual lands and grooves.
Using these parameters, firearm examiners can
search through a database of known rifling
data.
A typical GRC search:

a 9mm LUGER bullet, fired from a 6/right
rifled barrel, with a land width of .055 and
a groove width of .125.
Results of Search:
CARTRIDGE
MANUFACTURER
TWIST L&G
LAND
GROO
VE
9MM LUGER
AA ARMS INC
R
6
.055
.120
9MM LUGER
ASTRA
R
6
.053
.128
9MM LUGER
BERETTA
R
6
.055
.130
9MM LUGER
HI-POINT FIREARMS
R
6
.055
.120
9MM LUGER
INTERDYNAMIC
R
6
.055
.124
9MM LUGER
LLAMA
R
6
.054
.120
9MM LUGER
MAUSER
R
6
.054
.128
9MM LUGER
SMITH & WESSON
R
6
.056
.122
9MM LUGER
STAR
R
6
.054
.126
9MM LUGER
SWD INC
R
6
.055
.120
FBI Database:
The database used by firearm examiners
all over the world is compiled and
maintained by the FBI.
 The FBI has been recording rifling data
from firearms for over 20 years.
 As new firearms are manufactured, the
rifling data is included in the database.

Case Study

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Many years ago, a double murder occurred in
our community. An elderly couple was found
shot to death in their home by their son.
It appeared from the scene that there had been
a break-in but the son was immediately a
suspect. Investigators had a feeling that the son
may have committed the crime but could not
determine if he had owned or had access to a
firearm.
Bullets from the scene were examined and it
was determined that they were of 38 caliber and
were fired from an 8/right rifled barrel.
Case Study



A list of manufacturers was compiled and given
to the investigators.
Using this list, the investigators searched a
weekly "Bargain Mart" classified ad publication.
By calling the ads for firearms included on the
list of possibilities, the investigators found one
individual who said he had sold his revolver to
an individual who matched the description of the
son.
The son was then picked out of a police line-up
by the individual who had sold him the gun.
When confronted with the evidence the son
confessed to the killings.