Forensic Pathology for Police - Brainshare Public Online Library

Types of Weapons and Ammunition 339
Shotguns tend to have “smooth” bores, meaning the internal surface of the barrel
is not rifled but is smooth. The diameter of the barrel is referred to as the shotgun
gauge. From smallest to largest, examples of different gauge shotguns include .410,
20 gauge, 16 gauge, and 12 gauge. The “choke” of a shotgun refers to the extent
of constriction that occurs at the muzzle end of the barrel. From most constricted
to least constricted, the different terms used to describe choke include: full choke,
modified choke, improved cylinder, and cylinder.
Fig. 13.2 An unspent
(unfired) handgun cartridge.
The silver-colored casing
contains the unspent bullet,
which has a copper jacket
A “cartridge” is what many people might consider an “unfired bullet” (Fig. 13.2)
but an unfired bullet is, actually, only part of the cartridge that is used in handguns
and rifles. A cartridge is composed of a “casing” that contains in its base a primer (a
method for converting the trigger pull mechanism into ignition of the gunpowder),
the gunpowder itself, and the bullet, which is tightly embedded into the open end
of the casing (Disc Image 13.2). The two types of primers are the centerfire primer,
located in the center of the base of the cartridge, and the rim primer, located in the
outer rim of the base of the cartridge casing (Disc Images 13.3 and 13.4). The most
well-known rimfire ammunition is .22 caliber. When the firing pin strikes the primer,
the primer explodes and ignites the gunpowder and the exploding gunpowder expels
the bullet from the end of the cartridge. Traveling at a great velocity down the barrel,
the bullet is forced to spin along its longitudinal axis by the rifling of the inside
surface of the barrel. Besides the bullet, there are other items that travel down and
out of the barrel. Especially in handguns, the flames from the exploding gunpowder
can be seen at the muzzle (open end) of the barrel. Also, a cloud of smoke (soot)
created by the exploding gunpowder is expelled from the muzzle. Finally, particles
of unburnt as well as burning gunpowder are also expelled from the end of the barrel
(Fig. 13.3). The cartridge casing does not exit the weapon via the barrel. Depending
on the type of weapon, the casing may be mechanically ejected from the weapon,
or it may require manual removal. Usually semi-automatic weapons have a recessed
indentation just above the rim base, on the side of the casing, whereas revolver