Transcript Document

Firearms ID Presentation
Polson High School
What is Firearms
Identification?
Sometimes incorrectly referred
to as ballistics.
•The identification of fired
bullets, cartridge cases or
other ammunition components
as having been fired from a
specific firearm.
•Firearms identification is
actually a form of Tool Mark
Identification.
•Firearms evidence submitted to a
lab's Firearms Section will typically
include a firearm, fired bullets,
spent cartridge cases, spent shot
shells, shot, shot shell wadding, live
ammunition, clothing, and most
anything else.
In addition to comparing ammunition
components to firearms, firearm
examiners conduct other examinations
that usually include the following:
•Testing firearms
to determine if
they function
properly.
•Determine caliber and
manufacturer of ammunition
components. Including the
examination of various shotshell
components
•Determine the manufacturer or
manufacturers of firearms that
may have fired a particular bullet
or cartridge case.
Firearm Illustrations
Firearm
Illustrations
Pump Shotgun
Auto Shotgun
Bolt Action Rifle
All cases that involve firearms
identification start with preliminary
examinations of the evidence for
similar class characteristics. Class
characteristics can be defined as:
•Intentional or design
characteristics that would be
common to a particular group or
family of items.
Such as:
•The class characteristics of firearms
that relate to the bullets fired from
them includes the caliber of the
firearm and the rifling pattern
contained in the barrel of the firearm.
•Cartridges and Cartridge cases on
the other hand are examined for
Unique level similarities in what are
called breech marks, firing pin
impressions, extractor marks,
ejector marks and others.
Let’s look at some marks and impressions…..
Breech Marks
•44 SPECIAL caliber
cartridge cases fired
in a TAURUS
revolver.
More Breech Marks
•12 GAUGE shotshells
•38 SUPER AUTO
cartridge cases
fired in a COLT
pistol.
•357 MAGNUM caliber cartridge
cases fired in a TAURUS revolver.
•357 MAGNUM
caliber
cartridge
cases fired in
a COLT
revolver.
Firing Pin
Impression
22 LR caliber
rimfire cartridge
cases fired in a
RUGER pistol.
Action
Marks
7.62x39mm
cartridge
cases fired
in an AK or
SKS Type
rifle.
•Bullets collected for comparison to a
specific firearm are examined first to
see if they are of a caliber that could
have been fired from the submitted
firearm. Then they are examined to
determine if the pattern of rifling
impressions found on the bullet
match the pattern of rifling contained
in the barrel of the questioned
firearm.
•If these class
characteristics
agree, the next
step is to try to
make a positive
match between the
unique
characteristics that
may have
transferred to the
bullet from the
barrel.
•GRC
Identification
•General rifling
characteristics or GRC
are the identified rifling
pattern (i.e. 8/right) and
the widths of the
individual lands and
grooves.in a barrel.
•What are Lands and Grooves?
The Pitch is the angle (tilt)
at which the rifling is cut in
the barrel.
Note these two bullets have different sized land
impressions. They were fired from different
weapons.
The Rate of Twist is referring to
the distance the rifling will travel
to complete a single complete
turn. Ex: 1 turn in 10 inches.
MANUFACTURE
CARTRIDGE
TWIST
L&G
LAND
.055
9MM LUGER
AA ARMS INC
R
6
9MM LUGER
ASTRA
R
6
9MM LUGER
BERETTA
R
6
66666
.055
9MM LUGER
HI-POINT FIREARMS
R
6
.055
9MM LUGER
INTERDYNAMIC
R
6
9MM LUGER
LLAMA
R
9MM LUGER
MAUSER
9MM LUGER
.
053
GROOVE
.
120
.128
.
130
.120
055
.
124
6
.054
.
120
R
6
.054
.
128
SMITH & WESSON
R
6
.056
.
122
9MM LUGER
STAR
R
6
.054
.
126
9MM LUGER
SWD INC
R
6
.055
.
.120
Land
Impression
Groove
Impression
•The images below show rifling
impressions on a 32 caliber
bullet at progressively
increasing magnifications.
•A submitted firearm will be
fired several times using a
water tank to obtain standards
from the firearm.
•To make
these
comparisons
the firearm
examiner will
use a
comparison
microscope.
Evidence
Bullet Land
Impressions
Match With
Those On
Test Fired
Standard
Bullet.
What about a
fragment?
Can you still determine the
GRC of the weapon?
Maybe... if you
have at least
one Land and
one Groove
impression.
Let’s say you
suspect the
weapon to be a
0.357 handgun.
You would divide the 0.357 by the
sum of the two impressions and
then multiply that value by pi.
Like this....
If the Land
impression
measures 0.055”
wide
and
the
0.055” Land
+0.130” Groove Groove
impression
0.185” Total
measures 0.130”
wide...
So...
if Pi = 3.14 and
the suspected
weapon
is
0.357
0.055” Land
+0.130” Groove then the formula
becomes...
0.185” Total
( 0.357 / 0.185 ) 3.14 = 6.05
So total L & G should be ~6
Firearm examiners routinely
examine a shooting victim's
clothing for bullet holes and
other evidence that may
allow for a determination of
the distance from the muzzle
of the firearm to the clothing.
•There are tests to determine
the firing distance by
examining the area around a
bullet entrance hole for
gunshot residues
•These examinations are
sometimes referred to as
muzzle-to-garment or
muzzle-to-target
distance tests.
•Gunshot residues can also be
emitted from areas of a
firearm other than the muzzle.
•Because the various elements
included in gunshot residues are
very small and lack mass they
lose their energy rapidly.
•Gunshot Residue can only
travel between 3 and 5 feet
out from the muzzle.
•The further gunshot residues
travel from the muzzle, the
broader and less
concentrated the pattern
becomes.
Gun Shot Residue &
Testing For Distance From Muzzle…..
Gunshot residue distance
standards are made by
firing the firearm, using
ammunition like that used
in the actual case, into
witness panels that consist
of white pieces of cotton
twill jean cloth.
How do we prove that the particles
around this bullet entrance hole are GSR?
•The first chemical test conducted is
called the Modified Griess Test
•The Modified Griess Test is a test to
detect the presence of nitrite
residues.
•The Modified Griess Test is the
primary test used by firearms
examiners to determine a muzzle-togarment distance.
•The exhibit being processed is
placed face down against a piece of
treated photo paper, with the
bullet hole centered on the paper.
•The back of the
exhibit being
examined is then
steam ironed
with a dilute
acetic acid
solution in the
iron instead of
water.
•The acetic acid vapors will penetrate the
exhibit and a reaction takes place between
any nitrite residues on the exhibit and the
chemicals contained in the photographic
paper.
The nitrite
residues will
appear as orange
specks on the
piece photographic
paper.
•A close-up of the results.
Q: What chemical test would be
used to detect any lead residues
present on the exhibit?
A: The
Sodium
Rhodizionate
Test.
Step #1
Spray with SR + water
solution
Q: What chemical test would be
used to detect any lead residues
present on the exhibit?
A: The
Sodium
Rhodizionate
Test.
Step #2
Residue turns dark
yellow/orange.
Q: What chemical test would be
used to detect any lead residues
present on the exhibit?
A: The
Sodium
Rhodizionate
Test.
Step #3
Spray on a buffer
solution
Q: What chemical test would be
used to detect any lead residues
present on the exhibit?
A: The
Sodium
Rhodizionate
Test.
Step #4
The background color
fades & pink appears
Q: What chemical test would be
used to detect any lead residues
present on the exhibit?
A: The
Sodium
Rhodizionate
Test.
Step #5
Blue = Lead
Add dilute Hydrochloric
Acid solution
•The above images show a car's
headrest with a sooty deposit around a
bullet entrance hole. The right image
shows the headrest after processing
with Sodium Rhodizionate and a buffer
solution.
Typical contact entrance hole
Bullet hole (angled)
Angled grazing bullet holes
made by a single bullet.
•Bullet Exit Holes
•Typical Bullet Exit Holes
Another Typical Bullet Exit Hole
The “Hand”gun of tomorrow ?????