Intro to Firearms
Ballistics
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Long Guns and Handguns
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Long guns
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Handguns
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Rifles fire bullets
Shotguns fire pellets (shot) or a single projectile
(slug)
Pistols are fired with one hand
Revolvers have a cylinder that holds usually six
cartridges
Automatic and Semi-automatic
Forensic Science: Fundamentals & Investigations, Chapter 17
Firearms and Rifling
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Grooves and ridges
(lands) in the barrel of a
gun produce the twisting
that adds accuracy
This leaves a pattern on
the bullet that is unique
Forensic Science: Fundamentals & Investigations, Chapter 17
Bullets, Cartridges, and Calibers
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Cartridge—a case that holds
a bullet, primer powder, and
gunpowder
The bullet, usually of metal, is
out front with the cartridge,
holding the primer and
propellant powders, behind.
Forensic Science: Fundamentals & Investigations, Chapter 17
How a Firearm Works
1. The firing pin hits the
base of the cartridge,
igniting the primer
powder
2. The primer powder sparks through the flash hole to
the main propellant supply
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Forensic Science: Fundamentals & Investigations, Chapter 17
How a Firearm Works
3. 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
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Forensic Science: Fundamentals & Investigations, Chapter 17
Caliber of the Cartridge
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Caliber—a measure of the diameter of the
cartridge
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In hundredths of an inch
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Common calibers include
.22, .25, .357, .38, .44, and .45
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Why should the caliber of ammunition
match the firearm that shoots it? If they do
not match, what could go wrong?
Forensic Science: Fundamentals & Investigations, Chapter 17
What is a bullet?
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“Bullet” refers to the projectile(s) which
actually exits the barrel of the gun when fired
Bullets vary in shape and composition
There exists hundreds of different types of
bullets
Most types are variations on three main
shapes & three basic compositions
Forensic Science: Fundamentals & Investigations, Chapter 17
Anatomy of a bullet
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The bullet (projectile) can be made of many
different things
The primer powder initiates the contained
explosion that pushes the bullet down the
barrel. The primer is struck by the firearm’s
firing pin that will strike the rim or bottom of the
cartridge
The anvil and flash hole provide the
mechanism of delivering the explosive charge
from the primer to the gunpowder
The headstamp on the bottom of the cartridge
casing identifies the caliber and manufacturer
Forensic Science: Fundamentals & Investigations, Chapter 17
What are the types of bullets?
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Forensic Science: Fundamentals & Investigations, Chapter 17
Round Nose
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Maximum penetration
Cheapest shape to manufacture
Easily loads into chambers
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Hollow Point
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Spreads or mushrooms on impact
Causes additional damage to target
Inhibits penetration
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Wad Cutter
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Used exclusively as a practice load
Minimizes penetration
Rips a hole in target paper which is visible by
the shooter
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Bullet Composition: Three Types
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Lead
½ Jacketed
Jacketed (Full metal jacket)
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Lead Bullets
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Cheap and soft
Dense
Easy to mold
Forensic Science: Fundamentals & Investigations, Chapter 17
½ Jacketed
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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
Forensic Science: Fundamentals & Investigations, Chapter 17
Full Metal Jacket
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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
Forensic Science: Fundamentals & Investigations, Chapter 17
What Makes Fired Bullets Unique?
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When a gun is fired, the barrel marks each
bullet with its own unique pattern of land and
grooves
By examining the lands and grooves, a bullet
investigator can match to the gun from which
it was fired
Forensic Science: Fundamentals & Investigations, Chapter 17
What Makes Fired Bullets Unique
(Cont’d)?
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Investigators compare bullets and spent
cartridge casings from a crime scene with
bullets and spent cartridges shot from the
suspected firearm
Forensic Science: Fundamentals & Investigations, Chapter 17
What Makes Fired Bullets Unique
(Cont’d)?
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Firing pin marks left on the spent cartridge
casings can also be used to identify a firearm
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Breechblock markings are another kind of
mark left on spent cartridge casings when
the firearm is shot
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Left on the bottom of the cartridge when the firing
pin hits it to fire the shot
Causes explosive force that pushes the bullet
forcasing backward against breechblock, which
prevents the cartridge from shooting toward the
user as it recoils
Forensic Science: Fundamentals & Investigations, Chapter 17
Markings
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Firing pin mark
Breechblock marking
Forensic Science: Fundamentals & Investigations, Chapter 17
What Makes Fired Bullets Unique
(Cont’d)?
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Other marks left on spent cartridge casings
include extractor and ejector marks
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Minute scratches produced as cartridge is placed
in firing chamber (via extractor) and removed from
chamber after firing (via ejector)
Forensic Science: Fundamentals & Investigations, Chapter 17
Striations
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Forensic Science: Fundamentals & Investigations, Chapter 17
Matching Procedure for Striations
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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
Forensic Science: Fundamentals & Investigations, Chapter 17
Matching Procedure for Striations
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Forensic Science: Fundamentals & Investigations, Chapter 17