Ballistic Evidence
Ballistics
• Ballistics  the study of bullets and
firearms
• Firearm  a weapon, such as a gun,
capable of firing a projectile using a
confined explosive
Firearms History
• Matchlock weapons
 Relied on wicks to carry a
flame to the gunpowder
• Flintlock weapons
Relied on sparks from a
piece of flint to ignite the
gunpowder
– Could be used in damp
weather
• Percussion weapons
Introduction of cartridges (a
casing that holds a bullet)
Gun Parts – The Barrel
Barrel of a gun is produced from a single rod
of steel that has been drilled through the
center
– Drill markings are different for each type of gun
produced
• IE. Shotgun barrels are different than a rifle barrel
– Have different purposes
– Can vary in length
– No two rifled barrels, even those manufactured in
succession, will have identical striation markings
Barrel
• Manufacturers also impress the barrel with
spiral grooves
 Known as rifling
• The surfaces of the original bore remaining
between the grooves are called lands
Barrel
Each gun manufacturer uses its own
technique and own signature amount of
lands and grooves
– Ex. Smith and Wesson uses five lands and
grooves twisted to the right
Caliber
Caliber of a rifle or handgun is the diameter of
the gun barrel
– Usually recorded in hundredths of an inch or in
millimeters
– Shotguns are measured by gauges
Hammer
Part of the gun that is responsible for
beginning the reaction of a bullet firing
is the hammer
Breechblock / Ejector
• Breechblock
– The rear part of the firearm barrel
Stops the bullet casing from flying through the
back of the gun
• Ejector
Spits out the empty shell casings to make
room for the next bullet
Bullet / Ammunition
Bullet is a combination
of a gunpowder and a
projectile
– Can be a single bullet or
can be hundreds of
buckshot
Back of the bullet
contains a firing pin
that once struck, ignites
the gun powder
Bullet
How A Firearm Works
A Review
• Pull the trigger and the firing pin of the firearm
hits the base of the cartridge, igniting the
gunpowder mixture
• Gases expand and bullet is propelled forward
and case is forced backward
• Bullet is expelled through the barrel – spinning
according to the land and groove pattern. The
spent casing is ejected from the rear of the gun.
Bullet projection
• As soon as the explosion occurs, the bullet is
expelled out through the barrel of the gun
• Bullet is spinning
– This is due to the lands and groves in the barrel
– This creates markings on the bullet
Opposite Reaction
• Bullet casing is forced backwards against
the breechblock
• Casing is the removed via the ejector
Casing Imprints
• Casings are indented
with the markings
from the weapon’s
firing and loading
mechanisms:
– Hammer
– Breechblock
– Ejector/extractor
Questions to Answer
1.
What type of firearm was used?
2.
What was the caliber of the bullet?
3.
How many bullets were fired?
4.
Where was the shooter standing?
5.
What was the angle of impact?
6.
Has the firearm been used in a previous crime?
Critical Firearms Evidence
• All of the items below are essential in
firearms investigation
– The bullet
– The weapon
– The serial numbers on the weapon
– The gunpowder on garments, around wounds,
and on hands
The Weapon
• Safety is of the utmost importance when
collecting the weapon
• When collecting a found weapon, it is best
to pick it up by the edges of the trigger
guard or by the checkered portion of the
grip
Weapon Comparison
• Once a gun is
collected, a test firing
is completed in water
to provide a point of
comparison for
evidence collected
with the crime
– Remember each
weapon will leave its
own unique markings
on the ammunition that
it is using (both bullet
and casing)
Weapon Serial Numbers
• Each weapon has a serial number associated
with it
– Used for registration and purchasing reasons
– Criminalists can track movement of weapons based
on serial number
• Most of the time, criminals try to remove the serial number
• Stamped serial numbers put stress on the metal
of the gun
– When an etching agent is poured on area, the
stressed areas dissolve faster than surrounding metal
and reveal the serial number
Collecting A Bullet
• If a bullet is found lodged in something, it
is best to remove the surrounding material
as to not disturb any of the striations made
• Investigator puts initials on nose or back of
bullet
• Wraps it in tissue paper to avoid
scratching during transfer
NIBIN
National Integrated Ballistics Network
• Combination of NIBIS and Drugfire
• United in 2000
• NIBIN networks allows ballistics identification to
be conducted on a local, national, or
international scale.
– This networking feature has been employed to
successfully link crimes between countries.
Measuring Distance
• In cases where a victim has suffered a
gunshot wound, it is important to
determine the distance from weapon to
victim / identify the location of the shooter
Distance is determined primarily by the
presence and distribution of certain
powder patterns or by the spread of a shot
(for a shotgun)
Gunshot Residue (GSR)
Primers in the
bullet contain a
blend of different
chemicals
Look for the
elements
Antimony and
Barium
Firearm Discharge
• When a firearm is discharged, unburned and
partially burned particles of gunpowder (in
addition to smoke) are propelled out of the
barrel, along with the bullet, towards the target
It is the distribution of gunpowder particles and other
discharge residues around the bullet hole that
permits an assessment of the distance from weapon
to target
Gunpowder Distribution Factors
• Factors that influence gunpowder residue
on the target:
– Barrel length
– Caliber
– Type of ammunition
– Type and condition of weapon fired
– Distance from weapon to target
• No GSR will be on target if further than 3 feet
Gunshot Residue Distribution
• Handling of a used firearm, the passage of
time, and the resumption of normal
activities following a shooting, gun shot
residue is usually redistributed to other
areas
– Becomes harder to trace back to original
weapon
Bullet Wipe
Dark ring around the
perimeter of the
entrance hole in a
target
– Consists of a mixture
of carbon, dirt,
lubricant, primer
residue, and lead
being wiped off of the
bullet
Gunshot Residue Detection
• Swab both the firing and nonfiring hand
with a 5% solution of nitric acid
or
• Use adhesive tape on the hands to pick up
the particles of residue
– Tape is put under scanning electron
microscope
– More specific than hand swabbing
GSR Detection
• Infrared photography – used to help find
GSR in difficult situations (dark clothing or
bloody clothing)
• Greiss test  chemical test to develop
patterns of GSR around bullet holes
– Photopaper is ironed over entrance area
– Paper is sprayed with chemical
• Turns GSR pink then blue-violet