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What is ballistics? Give 3
examples of how ballistics is used
in forensic science.
1
Introduction
Ballistic evidence helps explain:
What type of firearm was used.
The caliber of the bullet.
The number of bullets fired.
Where the shooter was.
Whether a weapon was fired recently.
If a firearm was used in previous crimes.
Forensic Science: Fundamentals &
Investigations, Chapter 17
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Chapter 17 Ballistics
By the end of this chapter you will be able to:
describe rifling on a gun barrel and explain how it
marks a bullet
explain barrel size and caliber
describe how bullets are test fired and matched
discuss the role of ballistics recovery and
examination at a crime scene
determine the position of the shooter based on bullet
trajectory
All Rights Reserved South-Western / Cengage Learning © 2009
Forensic Science: Fundamentals &
Investigations, Chapter 17
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History of Forensic Firearm Identification
1835 – London, England.
Mold mark used to make
bullet from molten lead
used as evidence in
homicide case
1863 – Examination of
the bullet type and design
used to shoot Gen.
Stonewall Jackson
showed he was shot by
one of his own men
1879 – Minnesota. Rifling
marks from a revolver
used in court to
differentiate two revolvers
1925 – The comparison
microscope is developed
by Philip Gravelle
Firearm Nomenclature
Slide
Barrel
Extracto
rTrigger
Hammer
Safety
Ammunition
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Bullets, Cartridges, and
Calibers
Bullets and cartridges are packaged together.
The bullet, usually of metal, is out front
with the cartridge, holding the primer and
propellant powders,
behind.
Forensic Science: Fundamentals &
Investigations, Chapter 17
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Bullet Design
“Bullet” refers to the projectile(s) which
actually exits the barrel of the gun when
fired
Bullets vary in shape and composition
There exist hundreds of different types of
bullets
Most types are variations on three main
shapes & three basic compositions
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Three Main Shapes
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Round Nose
Maximum penetration
Cheapest shape to manufacture
Easily loads into chambers
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Hollow Point
Spreads or mushrooms on impact
Causes additional damage to target
Inhibits penetration
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Wad Cutter
Used exclusively as a practice load
Minimizes penetration
Rips a hole in target paper which is visible
by the shooter
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Three Basic Compositions of Bullets
Lead
½ Jacketed
Jacketed (Full metal jacket)
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Lead
Cheap
Dense
Soft
Easy to mold
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½ Jacketed
A lead bullet coated with copper half way
up the exposed portion of the bullet
Used primarily for
hollow points
Copper improves
exit velocity
Lead promotes mushrooming
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Jacketed
A lead bullet completely coated in
copper
Copper improves exit
velocity
Used to hold the
shape of the bullet in
an effort to maximize
penetration
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Caliber of the Cartridge
Caliber is a measure the diameter of
the cartridge in hundredths of an inch.
Common calibers include .22, .25,
.357, .38, .44, and .45.
Why should the caliber of ammunition
match the firearm that shoots it? If
they do not match, what could go
wrong?
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Investigations, Chapter 17
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What happens to bullets when
they
are fired?
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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
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Down the Barrel
4.As a bullet
travels down the
barrel of a gun it
is twisted by the
lands and
grooves of the
barrel.
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Out of the Barrel
5.This rifling
causes the
bullet to exit
the end of the
barrel in a
spiral motion.
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Bullet Analysis &
Comparison
What are some
characteristics used to
identify & compare bullets?
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Striations
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Matching Procedure
Fire bullets from a suspected
weapon
With the aid of a comparison
microscope, compare these “test
fires” to the suspected bullets
Striations must be identical for a
positive match
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Comparison
Microscope
Two
scopesOne Field
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What happens to a bullet
when it hits a target?
•Most bullets tend to
mushroom when they
hit a target.
•Some bullets nearly
disintegrate.
•Left are bullet
fragments from a ½
jacketed hollow point.
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Not all bullets mushroom the same. A lot
depends on the speed and shape of the bullet,
and the characteristics of the target.
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Some more bullets recovered after
firing
The striations from the rifling are
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still visible
Gunshot Residues
Chemical testing often can detect gun shot residue
even if removal is attempted.
What does this mean for investigation?
Forensic Science: Fundamentals &
Investigations, Chapter 17
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Databases
Like fingerprints, there is a federal
database for firearms used in previous
crimes – NIBIN (National Integrated
Ballistics Network).
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Investigations, Chapter 17
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