Chapter 17 Ballistics
By the end of this chapter you will be able to:
 describe rifling on a gun barrel and explain how it
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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
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Forensic Science: Fundamentals & Investigations, Chapter 17
Introduction
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Ballistics – the study of bullets and firearms.
Firearms – weapon capable of firing a projectile
using a confined explosive as a propellant.
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
History of
Gunpowder and Firearms
 The Chinese invented gunpowder (KNO3,
charcoal, & sulfur) over a thousand years
ago.
 Muzzle-loading matchlocks, the earliest
firearms, used wicks to ignite the gunpowder.
 The cartridge (a case that holds a bullet,
primer powder, and gunpowder) followed.
 Cartridges were loaded into the breech – the
end of the barrel attached to the firing
mechanism.
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Forensic Science: Fundamentals & Investigations, Chapter 17
Long Guns and Handguns
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Long guns, i.e. rifles and shotguns, require two hands
for accuracy
Rifles fire bullets; shotguns fire small, round pellets or
a projectile called a slug.
Handguns fired with one hand are called pistols
Revolvers are pistols with a revolving cylinder that
holds 6 cartridges
Semiautomatics hold up to 10 cartridges in a
magazine (clip).
Semiautomatic fires one bullet per pull of the trigger.
Fully automatic fires repeatedly as long as the trigger
is pressed.
Forensic Science: Fundamentals & Investigations, Chapter 17
Assignment
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Working in pairs or groups of three, research
5 different types of ammunition (not different
calibers), describe each in terms of
appearance and usage.
Forensic Science: Fundamentals & Investigations, Chapter 17
Vocabulary
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Grooves – depressions
Lands – ridges
Both are found on the inside of a firearm’s
barrel and are created when the firearm is
manufactured
Rifling – the spiral pattern of lands and
grooves in the barrel of a firearm
Forensic Science: Fundamentals & Investigations, Chapter 17
Firearms and Rifling
 Grooves and lands in the barrel of a gun produce
the twisting that adds accuracy.
 This leaves a individualized pattern on the bullet.
 It is impossible to produce two identically rifled
barrels
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Forensic Science: Fundamentals & Investigations, Chapter 17
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.
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Forensic Science: Fundamentals & Investigations, Chapter 17
Anatomy of a Cartridge
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Bullet – composed of lead, copper, or
combination of other metals. Can be metaljacketed, hollow-point, plastic coated
Primer powder – initiates the contained explosion
that pushes the bullet down the barrel
Anvil and flash hole – provide the mechanism of
delivering the explosive charge from the primer
powder to the gunpowder.
Headstamp – on bottom of cartridge identifies the
caliber and manufacturer.
Forensic Science: Fundamentals & Investigations, Chapter 17
How a Firearm Works
1. Pulling the trigger causes the firing pin to hit
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the base of the cartridge, igniting the primer
powder.
2. The primer powder sparks through the flash
hole to the main gunpowder supply.
3. The main gunpowder supply ignites and the
pressure of the explosion pushes the bullet
from the casing into the barrel.
4. The bullet follows the lands and grooves
spiraling out of the barrel.
Forensic Science: Fundamentals & Investigations, Chapter 17
Caliber of the Cartridge
 Caliber is a measure the diameter of the
cartridge.
 These usually are hundredths of an inch.
 Common calibers include .22, .25, .357, .38,
.44, and .45. Europe uses metric scale i.e.
9mm
 Caliber narrows down the type of gun used
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Forensic Science: Fundamentals & Investigations, Chapter 17
The Study of Bullets and
Cartridge Casings
Matching lands
(elevations)
Matching
grooves
(indentations)
 Investigators compare bullets and spent
cartridges from a crime scene to those from
the suspected firearm.
 Weapon is test-fired into water or a gel
block so bullet is captured without damage.
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Forensic Science: Fundamentals & Investigations, Chapter 17
Marks on the Spent Cartridge
Casings
 Firing pin marks on a spent cartridge can be used
to match it to a firearm.
 The fire pin marks can appear on the rim or on
the bottom of the spent cartridge.
 Breechblock marks are produced as the cartridge
casing slams backward & strikes the breechblock.
 Other marks on spent cartridge casings are
extractor and ejector nicks on semi and fully
automatic weapons caused by loading and
ejection of the cartridges
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Forensic Science: Fundamentals & Investigations, Chapter 17
Firing Pin Match
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Activity 17-2 in text. Pg 512-513
Copy table on page 513 and fill it in looking
at the casings from three suspects
Then make a list of all of the recovered
bullets and the suspect it matches (A=2, B=1,
etc)
Answer Analysis questions and Further
Study.
Forensic Science: Fundamentals & Investigations, Chapter 17
Gunshot Residues (GSR)
 GSR - Particles of unburned powder and traces of
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smoke after gun is fired.
They can leave a trace on the hand, arm, face, hair,
or clothing of the shooter.
They can also leave a trace on the victim.
Chemical testing often can detect residue even if
removal is attempted.
The distance from the victim to the shooter can be
determined by examination of the residue pattern on
the victim.
Forensic Science: Fundamentals & Investigations, Chapter 17
Databases
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Firearms databases can be used to match
crime scene evidence to registered weapons
National Integrated Bullet Identification
System (NIBIS) records ballistics markings of
firearms used in previous crimes
Drugfire – FBI database that focuses on
cartridge casings
In 2000, they merged to form the National
Integrated Ballistics Network (NIBIN)
Forensic Science: Fundamentals & Investigations, Chapter 17
Database Opinion Paragraph
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Write a paragraph (at least 7 good,
thoughtful sentences) about whether law
enforcement should maintain a database of all
firearms that are manufactured or sold in the
U.S.
Forensic Science: Fundamentals & Investigations, Chapter 17
Calculating Trajectory
Trajectory – the path of the propelled bullet
 Helps determine where the shooter was located.
 If trajectory angle is downward, the shooter was
positioned above the target.
 Two reference points along the flight path are
needed to define the trajectory.
 Investigators can figure the shooter discharged
the firearm somewhere along that line.
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Forensic Science: Fundamentals & Investigations, Chapter 17
Trajectory
 Reference points can be bullet holes in objects
or victims.
 An entry point and exit point on a victim can be
used.
 Gunshot residue or spent cartridge casings can
be less specific reference points.
 Investigators can use lasers to trace a straight-
line path to help determine the position of the
shooter.
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Forensic Science: Fundamentals & Investigations, Chapter 17
Trajectory
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Can be difficult to determine
Bullet can ricochet, become damaged, or
does not provide a direct path for
measurement.
Targeting needs to be adjusted for very
distant objects due to gravity.
Forensic Science: Fundamentals & Investigations, Chapter 17
Wind shield
Distance along path of
bullet to window, 23.9”
Path of bullet
x
Trajectory
y
60 feet
Horizon
Distance along
horizon to
window, 23.5”
Distance to the window
=
Distance along horizon to window
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Distance to the shooter (x)
Distance to the building
With the distance to the building and the distance to
the shooter along the trajectory of the bullet, the
Pythagorean theorem can be used to determine the
height of the shooter above the horizon (not the
ground)
Forensic Science: Fundamentals & Investigations, Chapter 17
Bullet Wounds
 Why do entrance wounds tend to be smaller
than exit wounds?
 If the bullet penetrates clothing, fibers may be
embedded in the direction of penetration
 GSR usually only found near entrance wounds.
 If gun is fired with the muzzle touching victim’s
skin, the muzzle flash may burn the skin
leaving a mark
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Forensic Science: Fundamentals & Investigations, Chapter 17
Bullet wounds
 Bullets may not travel smoothly through
body; tumbling effect due to bones, organs
and other tissues encountered
 High speed bullet are more likely to pass
through
 Small caliber bullets tend to lodge within the
body (less mass, not necessarily lower
speed)
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Forensic Science: Fundamentals & Investigations, Chapter 17