Ballistics
1998--Deaths due to handguns
US 11,789
Germany 373
Canada 151
Australia 57
England and Wales 54
Japan 19
In 2004 there were 29,569 gun deaths
56 percent suicides
40 homicide
Introduction
• Ballistics- is the study of bullets and firearms
– Firearm = a weapon, such as a gun, capable of firing a
projectile using a confined explosive
• Questions that can be answered by analysis of
ballistic evidence
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What type of firearm was used?
What was the caliber of the bullet?
How many bullets were fired?
Where was the shooter standing?
What was the angle of impact?
Has this firearm been used in a previous crime?
History of Gun Powder and Firearms
• Gunpowder invented over 1,000 yrs ago by chinese
– Gunpowder is a mixture of potassium nitrate (saltpeter),
charcoal, an sulfur
– When ignited gunpowder expands to six times its original size
causing a violent explosion
• Matchlock –used wicks to ignite the gunpowder
• Flintlock
– Muzzle (barrel) Loaders
• Gunpowder and projectile packed
down barrel
– Barrel = the long, metal tube that
guides a projectile out of the
firearm
– Muzzle = end of the barrel of a
firearm
• Percussion
•
Cartridge and bullet
Long Guns and Handguns
• Long Guns
– Rifles- fire bullets
– Shotguns- fire either small round pellets (shot) or a single projectile called a
slug
• gauge = the number of lead balls matching the barrels diameter that it takes to weigh
one pound
• Handguns
– Pistols- handguns that can be fired with one hand
• Single shot initially
• not as powerful and/or accurate as rifles
• Today, can be classified as revolvers or semiautomatics
– Revolvers- have a cylinder which contains several cartridges that can be fired in rapid
succession
» Invented by Samuel Colt, patented in 1835
» Cylinder can hold several cartridges
– Semiautomatic
» Hold 10 cartridges in one magazine (clip)
• Fire one bullet per pull of trigger
• The empty cartridge ejects and the next cartridge advances automatically
– Fully automatic
» Fire repeatedly as long as trigger is pressed
Firearms and Rifling
• An archer will hit a target with greater
accuracy if there is a twist on the end
of the arrow feathers
• Same applies to guns and bullets
– Barrel has lands and grooves
– Rifling = spiral pattern of lands and
grooves in the barrel of a firearm
• Lands = raised area
• Grooves = indentations
– Lands and grooves cause bullet to spiral
like a football
– The “rifling pattern” left on the bullet is
specific to each firearm
• No two guns, even of same model, are
rifled the same when made
• Provides individual evidence
Anatomy of a Cartridge
– Cartridge = a case that holds a bullet, primer powder,
and gunpowder
– Shell Casing = the metal (usually brass) housing from
the gunpower of a firearm
– The bullet can be composed of lead copper, or a
combination of various metals
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Lead
Lead alloy (lead mixed w/ other metals
Semijacketed- thin layer of brass coating
Fully jacketed-jacketed-completely covered with brass
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Greater penetration power
– The primer powder mixture initiates the contained
explosion that pushes the bullet down the barrel
•
Struck by firing pin of firearm, pressure caused ignition
– The anvil and flash hole provide the mechanism of
delivering the explosive charge from the primer
powder to the gunpowder
– The headstamp on the bottom of the cartridge case
identifies the caliber and manufacturer
How a Firearm Works
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Pull the trigger and the firing pin of the
firearm hits the base of the cartridge,
igniting the primer powder mixture
The tiny explosion (not much more than
a spark) of the primer powder misture
on the anvil delivers a spark through the
flash hole to the main gunpowder
suppy
The main gunpowder supply ignites,
and the pressure of the explosion
pushes the bullet from the casing and
into the barrel of the firearm. The
amount of gunpowder and mass of
bullet determines the speed of the
bullet
The bullet follows the lands and grooves
pattern of the barrel and begins to
spiral before it leaves the barrel
Caliber of the Cartridge
• Caliber- a measure of the inside diameter of a
firearm barrel
• Bullets (and their cartridges) are name by caliber
and length.
• The caliber is a measure of the diameter of the cartridge.22,
.25, .357, .44, and .45 are common calibers
– Example .45 = 45/100 of an inch
• European method using metric system (example 9mm)
– Bullet removed from wound or crime scene can be
linked to a gun by its caliber size
Marking on Bullets
• Lands and grooves rifling pattern in barrel of
gun leaves a unique pattern on bullet
– suspected weapons can be test fired and bullets
compared for individualizing evidence
Marks on a Spent Cartridge
• Marks left on bottom of cartridge by firing pins, can be
analyzed
• Breechblock marks are produced on cartridge as it travels in
opposite direction of bullet
– Breech is the rear part of a firearm barrel
• Where cartridge is loaded, opposite muzzle
– Cartridge hits breech block and mark is left
– suspected weapons can be test fired and cartridges compared
for individualizing evidence
• Some other marks
– Extractor and Ejector marks
• Extractor – mechanism that places cartridge into chamber of firearm
• Ejector – mechanism that removes cartridge from chamber after
firearm has fired
Gunshot Residues
• All firearms explode gunpowder and produce
gunshot residue (GSR)
– Residues are traces of smoke and particles of
unburned powder carried sideways from the firearm
by the expansion of gases as the bullet is fired
– Gunshot residues contain nitrates and metals
– Residues stick to the person holding the firearm and
leave evidence on the shooter
– The amount of GSR on the victim decreases as the
distance between shooter and victim increases
Trajectory
• Trajectory is the path of the for the propelled bullet
– Used to determine the position of a shooter
• Trajectory can be calculated by finding two or more
reference
• If ignoring gravity, it can be assumed that projectiles
such as bullets travel in straight lines
• Reference points can be
– bullet holes in objects or victims
– An entry point and exit point on a victim
– Gunshot residue or spent cartridge casings
• Lasers can trace a straight-line path to determine the
position of the shooter
Gravity and Trajectory
• Two major forces acting on a bullet after it
has been fired
– Forward force of the gunshot and
– Downward force of gravity
• If shot from close to medium distances
gravity can be negated in calculation of
trajectory
• Gravity needs to be accounted for if shots are
fired from greater distances
Determining Location of Shooter
Building is 60 feet away along the horizon line
Bullet hole is 4 feet above the ground
Where is the shooter located?
Triangulation
• B is where the shooter is located; find the length of BC
• The Abc triangle has the same proportions as the ABC triangle
Ab AB

• So
Ac AC
• AB = 732.3”

or
23.9" AB

23.5" 720"
Triangulation
• Using Pythagorean’s theorem
AB2 = AC2 + BC2
• 732.32 = 7202 + BC2
• BC2 = 732.32 – 7202
• BC2 = 536117 – 518400
• BC = √17717 (square root)
• BC = 133.1 inches
• BC = 11.1 feet
We know that the
bullet hole in the seat
is four feet above the
ground, so the shooter
is 15.1 feet above the
ground
Sample 1
• Ab = 32”
• Ac = 24 “
• CALCULATE BC
Building is 40 feet away along the horizon line
Bullet hole is 4 feet above the ground
Sample 2
• Ab = 22”
• Ac = 14“
• Calculate BC
Building is 20 feet away along the horizon line
Bullet hole is 4 feet above the ground
Solving When Angle is Known
• Tan (angle) = Opposite/Adjacent
Bullet Wounds
Why do entrance wounds tend to be smaller than exit wounds?
Bullet enters body small
May pick bone and tissue as it travels through body
tumbling effect
If the bullet penetrates clothing, what can fibers embedded in the
wound indicate?
entrance vs exit wound
Where is gunshot residue usually found?
usually only around entrance wounds
If the gun is fired with the muzzle touching the victim’s skin, what
telltale mark may show up?
burn mark on skin
Will larger or will smaller caliber bullets tend to lodge within the
body rather than passing through? Why?
smaller caliber-less velocity (speed)