08 AGAR (DO NOT DELETE) 3/31/2022 2:32 PM
2022] THE SHADOW OF PCAST 97
A cartridge, or round of ammunition, is composed of a
primer, a cartridge case, powder, and a bullet. The primer, a
metal cup containing a detonable mixture, fits into the base
of the cartridge case, which is loaded with the powder. The
bullet, which usually consists of lead or of a lead core
encased in a higher strength metal jacket, fits into the neck
of the cartridge case. To fire the bullet, the cartridge is placed
in the chamber of a firearm, immediately behind the
firearm’s barrel. The base of the cartridge rests against a
solid support called the breech face or, in the case of a bolt-
operated weapon, the bolt face. When the trigger is pulled, a
firing pin strikes a swift, hard blow into the primer,
detonating the priming mixture. The flames from the
resulting explosion ignite the powder, causing a rapid
combustion whose force propels the bullet forward through
the barrel.
The barrels of modern firearms are “rifled,” that is, several
spiral grooves are cut into the barrel from end to end. The
purpose of the rifling is to set the bullet spinning around its
axis, giving it a stability in flight that it would otherwise
lack. The weapons of a given make and model are alike in
their rifling characteristics; that is, number of grooves,
number of lands (the raised portion of the barrel between the
grooves) and twist of the rifling. When a bullet is fired
through a barrel, it is engraved with these rifling
characteristics.
In addition to rifling characteristics, every weapon bears
distinctive microscopic characteristics on its components,
including its barrel, firing pin, and breech face. While a
weapon’s rifling characteristics are common to all other
weapons of its make and model (and sometimes even to
weapons of a different make or model), a weapon’s
microscopic characteristics are distinctive, and differ from
those of every other weapon, regardless of make and model.
Such markings are initially caused during manufacture, since
the action of manufacturing tools differs microscopically
from weapon to weapon, and since the tools change
microscopically while being operated. As a weapon is used,