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Using Physics: Rifling and Ballistics
Ballistic gel is a special compound made to behave in a controlled
fashion when force is applied. Most often, ballistic gel blocks are
designed to respond to a gunshot in the same way a human body
would. The energy of the bullet passing through the gel is dispersed
at about the same rate it would be if the gel block were actually
flesh and bone. This helps ballistics experts determine the energy
of the bullet as it entered the victim.
the manufacturer relatively easily. Most major bullet manufacturers imprint
their bullets with a mark that is unique to their company, so identification is
a simple matter of finding the mark and matching it to sample bullets from
each company. This sounds tedious—and it used to be in the days before
the use of computer-database information storage. Today, a computerized
search can find a match very quickly, saving the analyst valuable time.
A similar method can be used to identify the make of the gun used. The
FBI maintains a database of manufacturer-provided information about the
markings guns leave on bullets and shell casings. Identification of the gun
is vital, because a bullet fired from one gun may not have the same flight
characteristics as the same bullet fired from a different gun. The energy the
bullet has as it leaves the barrel depends on such things as the length of
the barrel and the shape of the firing chamber in the gun.
After identifying the companies that produced the bullet and the gun, a
ballistics expert can begin testing to determine the energy of the bullet as
it leaves the barrel of the gun. For this, a special ballistic gel is used. Using
the same brand of gun as is suspected (or in some cases known) to have
been used in the crime, the expert points the gun at the gel and fires a bul-
