Operating Systems
Previous Section - Delayed Inertia (Delayed Blowback)
In recoil-operated systems the bolt and barrel are locked together
and free to recoil for a certain distance.
In short recoil they remain together only a small distance,
usually a few millimeters for pistols or the distance of a few
calibers for machine guns.
Reaching that point, the barrel stops recoiling and bolt
continues.
Short recoil designs can be further divided into
those that decelerate the barrel and those that
accelerate the bolt.
In either case the change of relative velocities means the
bolt and barrel separate (they relatively accelerate apart),
beginning case extraction.
As with inertia operation, cycling energy comes from recoil
forces, this time applied to both the free-moving barrel and
bolt masses, rather than the bolt alone as in inertia arms.
Deceleration can be accomplished by unlocking the bolt
from the breech and simply stopping the movement of the
barrel. This is the method used in the John Browning-designed
M1911 ("Colt .45") pistol and the vast majority of modern
semi-automatic pistols 9mm and larger (Glock, Smith and Wesson,
FN/Browning Hi-Power, SIG Sauer), which are largely derived
from his design. In the M1911 a movable link
tilts the barrel down and out of engagement with slide recesses.
The Hi-Power, Glock and other recent designs simplify this
by utilizing a downward-angled ramp on the barrel/chamber
which contacts a fixed stud in the frame, moving the barrel
down and out of engagement with the slide. In both cases
the link or stud also arrest the barrel's rearward movement,
with the slide continuing on and extracting the spent case.
Today, the most common short recoil designs where the bolt
is accelerated are John Browning's .30 and .50 caliber (7.62 and
12.7mm) M2 machine guns.
The .50 caliber M2 is still in wide use in western countries,
where it can be found for example on the cupola of the M1 Abrams tank.
In the M2 machine gun, a cam track in the
receiver moves a rectangular breech lock on a barrel extension
out of engagement with the bolt during the first 10 millimeters
of recoil.
The barrel extension then strikes a short, curved lever
which through mechanical advantage accelerates the bolt
rearward. The extension and attached barrel halt when
the extension encounters a stop, while the bolt continues rearward.
In recoil operation the bolt and barrel are locked together
initially. In the most successful deceleration and acceleration
short recoil designs, namely Browning's M1911 pistol and M2 machine gun,
locking is accomplished
by tipping the barrel or sliding a lock vertically in
the bolt. In his other designs bolts lock the breech by
tipping into receiver recesses. Linear or tilting locking
motions rather than bore-axial rotary locking could perhaps be
said to be one trademark of Browning designs.
It's perhaps worth noting that Browning was one of the
pioneers of automatic firearms. His designs are arguably
some of history's most successful. When America joined
the fight against totalitarian domination of Europe in World War I,
Browning donated his designs to the war effort of the
United States,
rather than profiting greatly by licensing them.
John Browning's deep devotion to the principles of freedom
led him to this.
Next Section - Long Recoil
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