Automatic and semiautomatic weapons are
The extracting action pulls the empty case out of the
classified by how they obtain the energy required for
chamber. The extractor (normally a small hooked piece
operation. Fundamentally, small arms obtain their
of metal encased in the bolt) snaps over the rim of the
operating energy from the forces of the explosion
cartridge case when the round is chambered. As the bolt
created when a round of ammunition is fired. The use of
moves rearward after firing, the extractor hauls out the
these forces does not reduce the effectiveness of the
weapon; it simply uses otherwise wasted energy.
Methods of Operation
There are three basic types of operation for
In addition to being pulled out of the chamber, the
automatic and semiautomatic small arms--gas
case must also be thrown free of the receiver. This
operation, recoil operation, and blowback operation.
action is called ejection and is created by placing a small
projection on one side of the receiver so that, as the bolt
and case move to the rear, the case will strike the
GAS OPERATION.--In gas-operated weapons, a
projection and be expelled from the weapon. This
portion of the expanding powder gases behind the bullet
method is used in the .45-cal. pistol. Another method of
is tapped off into a gas cylinder located beneath the
ejecting the case is to incorporate a spring-loaded
barrel. (The hole connecting the barrel and cylinder is
ejector in the face of the bolt. In this arrangement the
near the muzzle end.) As the bullet passes this hole,
gases push this piston rearward. The piston is
case is flipped from the weapon as soon as its forward
connected by a rod to an operating mechanism of the
end clears the chamber. This method is used in the M14
weapon, such as the bolt. The piston carries the bolt
rearward with it, unlocking the bolt, extracting and
ejecting the case, and cocking the weapon.
RECOIL OPERATION.--As a round is fired,
Cocking is the retraction of the firing mechanism
high pressures develop behind the bullet and force it
(firing pin and hammer) against spring pressure so that
down the barrel. The force behind the bullet is also
there will be sufficient energy to fire the cartridge in the
directed rearward against the breech. If the barrel and
next cycle of operation. The firing pin, hammer, or, in
bolt are secured to one another, the entire force of recoil
some cases, the bolt itself is held in a cocked position by
is felt on the shooter's shoulder. But, by designing the
a piece called the sear.
barrel and breech assembly so they can slide in the
Firing is initiated by squeezing a trigger. This
frame or receiver, the energy of the rear moving
movement trips the sear, releasing the firing mechanism
assembly can be used to compress springs, move levers,
(firing pin, hammer or, in automatic weapons, such
and so on, necessary to complete the cycle of operation.
parts as the bolt group), causing it to move forward with
enough force to discharge the round.
AND SEMIAUTOMATIC FIRING
A semiautomatic weapon unlocks, extracts, ejects,
cocks, and reloads automatically. However, the trigger
must be pulled each time to fire a round. By this
d e f i n i t i o n , the .45-cal. M1911A1 pistol is
semiautomatic, though it is often called automatic. A
fully automatic weapon keeps on firing as long as the
trigger is kept pulled.
Two examples of weapons that can be fired both
automatically and semiautomatically are the 7.62-mm
M14 rifle and the 5.56-mm M16 rifle.
Figure 2-2.--Types of operating systems.