cannot sustain the continuous rate of fire required by
that particular diameter required to make a pound. For
machine guns. Therefore, machine gun ammunition is
example, if you measure the diameter of a 12-gauge
belted, and the rounds are fed to the rear of the chamber
shotgun's bore, you will find it to be 0.729 inch. If you
by cam and lever action.
were to make a number of lead balls of this diameter and
weigh them, you would find that 12 of them make a
So the larger the bore of a shotgun, the smaller the
The locking action holds the bolt in its forward
gauge number. A 16-gauge shotgun, for example, has a
position for a short time (after firing) to prevent the loss
smaller bore than a 12-gauge.
of firing gas pressure until the bolt is unlocked by other
forces. For low-power weapons, it is possible to seal the
CYCLES OF OPERATION
breech for a short time by merely increasing the weight
of the bolt. The bolt starts to move as soon as the
Every weapon has a cycle of operation. This cycle
weapon fires. But if the bolt is sufficiently heavy, it
is a group of actions that takes place when a round is
will not move far enough to release the gases until their
fired and that must occur before the next round can be
pressure has been satisfactorily reduced. This method is
fired. In the automatic small arms currently used by the
used by submachine guns and other straight blowback-
Navy, the sequence of actions or the way they take place
operated small arms such as .22-cal. rimfire autoloading
may vary between weapons of different design;
however, they always occur.
There are eight steps in the cycle of operation, as
The firing action occurs when the firing pin strikes
the primer of the cartridge.
The feeding action places a round in the receiver
Unlocking occurs after the firing of the round.
just to the rear of the chamber. In its simplest form it
Actions for unlocking are just the reverse of those
amounts to putting a cartridge by hand in the path of the
required for locking. For most rifles, the first movement
device that will chamber the round. Most often, feeding
of the bolt is a rotating movement that disengages the
is done by a spring-loaded follower in a magazine.
However, magazines have a limited capacity that
Figure 2-1.--The small arms cycle of operation.