This document provides information about firearms and toolmarks analysis in crime scene investigations. It describes key parts of guns like the barrel, cartridge case, slide, and firing pin. It explains how guns work and the components of cartridges, including the primer, smokeless gunpowder, and projectile. It also details characteristics of bullets like rifling impressions, striations, caliber and rifling number that examiners analyze to determine if a specific gun was involved in a shooting. Class characteristics refer to marks that are common to a brand or type of firearm, while individual characteristics are unique to a single firearm.

1. CSI Training
Firearms and Toolmarks
STEM: CSI Experience Activity
Supplemental Notes

2. CSI-Firearms and Toolmarks
• Parts of a Gun

3. CSI-Firearms and Toolmarks
• Semiautomatic
Handgun: A gun that
fires a single cartridge,
ejects spent cartridge
case, and reloads itself
each time the trigger is
pulled. A separate
trigger pull is required
each time the weapon
is fired.

4. CSI-Firearms and Toolmarks
• Barrel: A long tube the
bullet or projectile
travels through before it
exits the firearm.
– The barrel has many
shallow ridges, called
rifling, which helps the
bullet fly in a straight
line.

5. CSI-Firearms and Toolmarks
• Cartridge Case: A
container for all the other
parts of a cartridge- the
projectile, primer, and
propellant (gunpowder).
After the bullet has been
fired the “spent” or
empty cartridge case is
marked with that gun’s
unique individual
characteristics.

6. CSI-Firearms and Toolmarks
• Slide: The portion of a
semiautomatic firearm
that holds the firing
mechanism. After the
bullet is fired the slide
moves backwards to
eject the used cartridge
and automatically load
another.

7. CSI-Firearms and Toolmarks
• Firing Pin: The part of
the firearm that hits the
primer in a cartridge
and causes it to
explode. This initiates
the firing of the bullet.
The firing pin can leave
distinct marks on the
cartridge case.

8. CSI-Firearms and Toolmarks
• Magazine: A device
which holds the
cartridges and feeds
them one at a time into
the firing chamber of
the firearm.

9. CSI-Firearms and Toolmarks
• Rifling: Spiraling ridges
located inside the barell
of the gun. They cause
the projectile to spin as
it flies through the air,
which improves
accuracy. The rifling
also marks the bullet
with the gun’s unique
characteristics.

10. CSI-Firearms and Toolmarks
HOW A GUN WORKS
• When the trigger is
pulled.
• The hammer hits the
firing pin.
• The firing pin hits the
cartridge.

11. CSI-Firearms and Toolmarks
PARTS OF A CARTRIDGE
• Cartridge: A single
unit of ammunition
made up of a
projectile, propellant ,
and primer,
surrounded by the
cartridge casing. A
“blank” is a cartridge
without a projectile.

12. CSI-Firearms and Toolmarks
PARTS OF A CARTRIDGE
• Primer: A shock
sensitive chemical
mixture that explodes
when struck by the
firing pin. Sparks form
the primer ignite the
propellant and initiate
firing of the bullet.

13. CSI-Firearms and Toolmarks
PARTS OF A CARTRIDGE
• Cartridge Case: A
container for all the
other parts of the
cartridge, the projectile,
primer, and propellant
(gunpowder). After the
bullet has been fired the
“spent” or empty
cartridge is marked with
that gun’s unique
individual characteristic.

14. CSI-Firearms and Toolmarks
PARTS OF A CARTRIDGE
• Smokeless
Gunpowder: A
complex chemical
mixture that rapidly
burns when ignited by
a spark from the
primer. This produces
gases that rapidly
expand and force the
bullet out of the
firearm.

15. CSI-Firearms and Toolmarks
PARTS OF A CARTRIDGE
• Caliber: An
approximate
measurement of the
bullet’s diameter. For
example, a .45 caliber
bullet has a diameter
of 0.45 inches, and a
9mm bullet has a
diameter of 9
millimeters. (0.9
centimeters)

16. CSI-Firearms and Toolmarks
PARTS OF A CARTRIDGE
• Projectile: Any object
propelled by an
explosive reaction.
Bullets are specialized
projectiles designed to
be fast and accurate.
The size of the bullet is
measured by its caliber
(diameter).

17. CSI-Firearms and Toolmarks
Bullet Characteristics
• Stirations: Tiny,
microscopic scratches
on the surface of the
bullet, usually located
inside the rifling
impressions. No two
firearms will produce
exactly the same
pattern of striations.

18. CSI-Firearms and Toolmarks
Bullet Characteristics
• Rifling Impression:
Impressions left on the
surface of the bullet
after it has been fixed
from a firearm with a
rifled barrel. The rifling
impressions on a bullet
can be either
conventional (deep and
easy to see, as in the
picture) or polygonal
(smoother and harder
to see)

19. CSI-Firearms and Toolmarks
Bullet Characteristics
• Rifling Number: The
number of lands (raised
areas) or grooves in a
rifled barrel. The rifling
number of a particular
firearm can be
determined by rotating
the bullet and counting
the number of rifling
impression present on
the surface.

20. CSI-Firearms and Toolmarks
Bullet Characteristics
• Rifling Direction: Rifling
grooves can spiral either
to the left or right;
making the bullet spin
either clockwise or
counterclockwise in the
air. The direction of the
rifling is determined by
the direction of the
grooves as they move
from the base to the top
of the bullet.

21. CSI-Firearms and Toolmarks
Bullet Characteristics
• Firearms Examiners use
two types of bullet
characteristics to
determine if a bullet
could have been fired
by a certain gun:
• What would not be a
class characteristic??
• Striations, caliber,
Rifling Direction, or Rifle
Number
• Class Characterisitcs:
Specific for a certain
brand or type of
firearm.
• Individual
Characteristics: Specific
for an INDIVIDUAL
firearm.

22. CSI-Firearms and Toolmarks
Class Characterisitics
• Firearms Examiners use
two types of bullet
characteristics to
determine if a bullet
could have been fired
by a certain gun:
• Class Characterisitcs:
Specific for a certain
brand or type of
firearm.
• Individual
Characteristics: Specific
for an INDIVIDUAL
firearm.