TRAINING LAB – FIREARMS AND BALLISTICS: BARREL AND BULLET
STRIATIONS
NAME___________________________________________
Background: You have learned
... [Show More] that the inside of a firearm’s barrel contains lands and
grooves in a twisting pattern, which forces an exiting bullet to spin. The pattern of lands
and grooves can help you determine the manufacturer of a firearm – an example of Class
Evidence. You may also recall that many small scratches or STRIATIONS are left behind in
a firearm’s barrel during the process of manufacturing the lands and grooves – and that
each firearm has its own unique set of striation “fingerprints”. This is an example of
Individual Evidence. In this Training Lab you will continue your study of BALLISTICS (the
study of firearms and the bullets they fire) and investigate barrel and bullet striations in
more detail.
1. You will be trained to analyze the striation patterns on evidence bullets and
use this information to help solve a crime.
Procedures:
1. The striations in a firearm’s barrel are just like fingerprints – each with it’s own unique
pattern of striations. When a bullet is fired it rubs against the inside of the firearm’s
barrel and picks up an imprint of the barrel’s unique striations. Find a bullet at a crime
scene and you can use the bullet’s striation marks to identify the gun that fired it.
2. You need two things to identify a gun that fired a bullet at a crime scene:
A. You need an evidence bullet that has visible striation marks. This can be a
problem because many times the bullet is destroyed when it hits an object –
fragmenting into many pieces or being smashed in a way that destroys the
striations. However, you can still match an evidence bullet to a gun if only a
portion of the evidence bullet contains striation marks.
B. You need the firearm that you think may have fired the bullet. It is difficult to
actually check the striations inside a gun’s barrel to compare them to an evidence
bullet’s striations. It’s much easier to fire another bullet from the suspect gun and
compare the striations on this known bullet to the striations on the evidence
bullet to see if they match. The known bullet is usually shot into a large tank of
water where it can be collected without any damage.
3. Now, let’s put your ballistic skills to work and solve the following crime!
THE MYSTERY OF THE SEXTUPLET MURDER
You arrive at 4680 Barberry Drive and discover a murder. Bobby Barrister, 32 years old,
was shot ONCE in the chest while sitting on the couch in his living room. You also observe
FOUR other bullet holes in the living room, however, none of these shots hit Bobby (see
Figure 1 for a sketch of the crime scene). Bullet Evidence #1 and #2 were found in the
wall behind the couch, Bullet Evidence #3 and #5 were found in the couch, and Bullet
Evidence #4 passed through Bobby’s body and entered the couch. You carefully remove all
FIVE bullets for analysis. [Show Less]