The big picture of ballistics
Because every contact leaves a trace (Locard’s
exchange principle) very hard contacts (like a
180 mps to 1500 mps contact) will leave a
Gunpowder and Firearms
The Chinese invented gunpowder over a
thousand years ago.
Muzzle-loading matchlocks used wicks to
ignite the gunpowder.
The cartridge and breech loading followed.
Rifling provided greater accuracy.
Revolver, semi-automatic, and automatic
handguns were developed.
– The study of projectiles, trajectories,
and the effect on the target
– A sub-discipline of ballistics that
determining whether a bullet or
cartridge was fired by a particular
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.
A Internal ballistics
What happens in the weapon
B External ballistics
What happens after the bullet leaves the
C Terminal ballistics (wound ballistics)
What happens when the bullet hits the target
A Internal ballistics (1 of 3)
SO WHAT’S A CARTRIDGE?
a combination of:
– a projectile (the bullet)
– a propellant (gunpowder, for example)
– a primer (the explosive cap),
The bullet, usually made of metal, is out front
with the cartridge, holding the primer and
propellant powders, behind.
Watch this short video
How a gun 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.
3. The pressure of the explosion pushes
the bullet from the case into the barrel.
4. The bullet follows the lands and grooves
spiraling out of the barrel.
Land = high
BACK OF BULLET
Groove = Low
ABROACH CUTTER USED
TO CREATE RIFFLING
IMPRESSIONS IN A
As a result of rifling, a barrel will impress a
negative impression of itself on the sides of
the bullet like those seen below.
A fired bullet as class evidence
Different gun manufacturers use different
rifling techniques. These techniques
impart the class characteristics on a fired
– Number of impressions
– Width of impressions
– Depth of impressions
– Angle of impressions
Q: How are these 2 guns different
What is caliber?
Caliber = the diameter of the bullet.
Measured in hundredths of an inches.
– .22, .357, or .50
Measured in metrics
Question: Why should the caliber of ammunition
match the firearm that shoots it? If they do not
match, what could go wrong?
Showing variation within caliber
INTERNAL BALISTICS (2 OF 3)
BREECH MARKS ARE
FOUND ON THE
REAR OF A FIRED
When a bullet is fired, the explosion forces:
1. the bullet down barrel
2. the cartridge back against breech
– Leaving a negative impression on the back of
Depending on the
make of gun & normal
wear and tear, the
breech markings will
pick up class, and
Examples of breech markings
How CSI determines if a recovered
bullet from a crime scene came
from a suspected gun
Disclaimer: this video is oooooold
Shotguns have smooth barrels with no rifling.
– Are there lands or groves on the bullet(s)?
How can a F.S. identify trace evidence left by
– Only by marks on the spent shell casing(s):
Shotgun into ballistics gel
External ballistics is
everything that happens after
the bullet leaves the gun to just
before the BULLET impacts its
GUN SHOT RESIDUE
GUN SHOT RESIDUE
CAN BE DETECTED
EVEN AFTER WASHING
CLOTHING / HANDS
Particles of unburned powder and traces
of smoke are the residues of gunshots.
They can leave a trace on:
hand, arm, face, hair, or clothing
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
Distance along path of Path of bullet
bullet to window, 23.9”
60 feet Horizon
2 Reference points needed to
– can be bullet holes in objects or victims.
Investigators can use lasers to trace a
straight-line path to help determine the
position of the shooter.
Point of impact
Point of initial Point of secondary
Point of aim
5 Ballistic Terms
PII – Point of Initial Intersect. Where the bullet crosses the
LOS (Line of Sight) for the first time.
MO – Maximum Ordinate. The highest point the bullet
reaches during its parabolic flight path.
PSI – Point of Secondary Intersect. The point where the
bullet crosses the LOS for the second time.
POI – Point of Impact. The point where the bullet impacts the
POA – Point of Aim. Where the shooter was aiming the
If the sights are properly adjusted:
POI = POA = DOA (dead on arrival)
C Terminal ballistics
1. Why do entrance wounds tend to be smaller than exit
2. If the bullet penetrates clothing, what can fibers
embedded in the wound indicate?
3. Where is gunshot residue usually found?
4. If the gun is fired with the muzzle touching the victim’s
skin, what telltale mark may show up?
5. Will larger or will smaller caliber bullets tend to lodge
within the body rather than passing through? Why?
GUN SHOT RESIDUE
Bullet wounds (4 kinds)
1. Barrel on skin
2. Barrel just off skin
3. Barrel inches away
4. Shot from a distance
Barrel on skin
Distinctive star pattern, so…
energy from the gun shot
forced back out entryway
NO burnt gun powder marks
around entryway, so…
•ALL gunpowder delivered
inside entryway singing the
interior (black area)
Barrel inches away
bullet entry way
No star pattern
– No “blow back”
Barrel just off skin
- no star pattern so..
– not ON skin
No stippling from g.p. so..
– TOO close for inches away
Barrel burns like on skin
– JUST off skin
9mm to person’s back NOTICE:
– Lack of burnt gun powder burns on skin
– Lack of star pattern
Conclusion = shot from distance
(probably through clothes)
Shot from distance
(but photo shopped)