WARMUP
• How can impression evidence help us solve a
crime?
• What are different types of impression
evidence?
Assassination of JFK
FIREARMS
UNIT 3
The Ten Commandments of Gun Safety
Random Fact!!!
• In 2004, there were 29,5769 gun deaths in the
U.S.
• Suicides accounted for 56%
• Homicides were 40 %
In 1998, handguns
killed….
• 373 people in Germany
• 151 people in Canada
• 57 people in Australia
• 54 people in England and Wales
• 19 people in Japan
11, 789
People in the U.S. were killed with handguns in 1998
When did firearm
production begin??
•Gun powder
invention
CHINA in
in______
the second
century A.D.
TYPES OF
FIRARMS
Handguns or Pistols
• Designed to be held in
one hand
• Easy to _______
and
Carry
conceal
• Not as accurate as
other firearms
• Limited to the number
of bullets they can hold
2 Types of Handguns
Revolver
• Cylinder that holds 6
bullets
• Has to be reloaded by
hand
• AKA
• “SIX-SHOOTER”
Semiautomatic
• Shoots one cartridge
each time the trigger is
pulled
• Reloads automatically
• Holds between 5 and 19
rounds
Revolver and
Semiautomatic
Revolver
Semi-automatic
What is the difference
between semi-automatic
and fully automatic????
•A fully automatic weapon keeps
firing as long as the trigger is
held back
•Machine gun is a good
example of this
Rifles
• Longer barrel than
handgun
• Butt stock that fits to
the shoulder to steady
the firearm and
minimize kickback
• Shoot more powerful
cartridges than
handguns
Shotguns
•Similar to
rifles, but
used to
shoot a
packet of
spherical
pellets
Air Guns or BB Guns
•Shot or pellets
are propelled
by pressurized
air, spring
compression,
or carbon
dioxide
cartridge
warmup
• Why is weapon identification a significant
source of crime scene information?
DAY 2
AMMUNITION
© Precision Forensic Testing
Types of Ammunition
• Modern ammunition consists of
•
•
•
•
Cartridge Case
Primer
Propellant
Projectile
Bullet Type
Bullet Vocabulary
• Caliber- measure of the diameter
• Bore- inside diameter of the bullet
• Gauge- Size of a shotgun, related to the weight of the
lead pellets
• Slug- Single pellet
Types of Bullets
Three Main Bullet
Shapes
Types of Rifling
• Cut Rifling -
Types of Rifling
• Polygonal Rifling -
Class Characteristics
• All class
characteristics are
measurable
• Caliber
• Number of lands and
grooves
• Width of the lands and
grooves
• Direction of twist
1
2
3
Measuring the Class Characteristics
• Caliber
• Number of Lands/Grooves
• Direction of Twist
• Width of Lands/Grooves
Measuring Caliber
• Using a vernier caliper, measure
the base of the bullet to the
hundredths of a millimeter.
11
• This bullet measures 11.50
millimeters
• Multiply millimeters by 0.0394
to determine inch measurement
.50
• 11.5 x 0.0394 = .453 (approx. .45
inches)
• Record your results
Types of Rifling
• Rifling is classified as
being either “Cut” or
“Polygonal”
• Polygonal (P) rifling
has a smooth
transition between
lands and grooves
• Cut (C) rifling has
defined shoulders
Polygonal Rifling
Cut Rifling
Counting the Lands and
Grooves
The grooves of the
bullet are counted
It may be necessary to
place a small mark with
a felt tip pen in the
location where
counting begins.
1
2
3
Direction of Twist
• The twist is determined by sitting the bullet on a
flat surface and observing the direction of the
rifling.
Left
Right
Width of the Lands and
Grooves
• Calipers are used to
measure the width of
the bullet lands and
grooves
Weighing the bullet
• The bullet weight is
recorded in grams
• Convert the weight from
grams to grains
• 1 gram = 15.43 grains
Bullet Type
Exercise #2: Determining the Possible Make of
Firearm Based on Class Characteristics
• Using the
measurements of the
class characteristics, a
list of possible makes of
firearms can be
established
Round Nose
• Maximum penetration
Hollow Point
• Least penetration
• Spreads on impact
• Causes additional damage to target
Hollow Point
Wad Cutter
• Used just for practice loads
• Creates a rip in paper that can be easily seen
by shooter
Class Evidence
• Weight of bullet
• Dimensions of bullet
• Shape of bullet
• Type of bullet
Individual Evidence
• Striae- parallel sets of scratches on a bullet
caused by unique markings in the bore of a
rifled weapon
• Like a bar code
Scratches on the cartridges caused by loading and
unloading in the magazine
Give it a try! Fired Bullet
Classifications!
DAY 3
What happens to bullets
when they
are fired?
bsapp.co
Pull the Trigger and . . .
1.A pin or hammer
strikes the primer.
This causes a spark.
2.The powder is then
ignited causing an
explosion.
3.This explosion starts
the bullet down the
barrel of the gun
bsapp.co
Down the Barrel
1.As a bullet travels
down the barrel of
a gun it is twisted
by the lands and
groves of the
barrel.
bsapp.co
Out of the Barrel
5.This rifling
causes the bullet
to exit the end of
the barrel in a
spiral motion.
bsapp.co
to
What happens to atend
bullet
mushroom
when it hits a target?
when they
hit a target.
Some
bullets
nearly
disintegrate
.
Left are
bullet
fragments
bsapp.co
Not all bullets mushroom the same. A lot
depends on the speed and shape of the
bullet, and the characteristics of the
target.
bsapp.co
bsapp.co
Some more bullets recovered
after firing
The striations from the rifling are
still visible
bsapp.co
Distance From Target
• Important to know distance from muzzle to
target in order to reconstruct the event
• As bullet leaves muzzle, it carries some of the
unburned particles along with as well as the
combustion products
http://www.youtube.com/watch?v=9mQ8tN561-Q
Greiss Test
• Nitrites are primary combustion product
• The Greiss Test can chemically convert nitrite to
colored products
Gunshot Residue
• Burned and unburned powder, vaporized and
particulate lead, primer residues of lead,
barium, and antimony
• GSR can be found on the shooter’s hand
How does manufacturing characteristics
of guns aid in the identification of
specific weapon and possible
perpetrator?
Forensic ballistics
is the application of ballistics
(characterizing firearms) to address
legal questions.
Ballistic
fingerprinting
refers to a set of
forensic techniques
that rely on marks
that firearms leave on
bullets to match a
bullet to the gun it was
fired with.
• Firing Mechanism (semiautonmatic, single action…etc.)
• Ammunition Traits (head stamp, shape, profile….etc.)
• Bullet type (boat tail, wadcutter…..etc.)
• Firearm Barrel characteristics (rifling, lands and
grooves….etc.)
• Trigger is pulled!
• The hammer withdraws
and rapidly strikes the
back of the bullet.
• The shock of the strike
causes an explosion of
the primer.
• The gunpowder
combusts.
• This propels the bullet or
slug.
• Most primer blends contain:
• Lead, antimony and barium.
• Other components can be
used.
Gun powder:
• Main ingredient cellulose
nitrate
• These materials causes
and exothermic reaction
and where heat escapes
so too does unused
material.
Your task: Test +/- and yourself!
SR
D