Page 81 - FAT 105 4.17 MOODLE

Figure 5b: Roller delayed blowback action.
move inward against the carrier ex-
tension and drive the carrier extension
and carrier backward. This happens
with so much force that the carrier
accelerates faster than the bolt head,
delaying the bolt head’s movement.
The rollers move inward, clearing the
cutouts in the receiver.
The carrier will continue to move
rearward, pulling the bolt head with
it, which, in turn, extracts the empty
case from the chamber, ejects it,
and cocks the hammer. The action/
recoil spring drives the bolt and car-
rier forward, stripping a round from
the magazine and feeding it into the
chamber. The bolt will bottom out
against the cartridge and the bar-
rel, while the carrier will continue to
move forward, driving the extension
into the rollers and forcing the rollers
into the cutouts in the receiver.
The roller delayed blowback action
allows the use of higher power car-
tridges while maintaining much of the
simplicity of the blowback action. The
delayed blowback action is capable of
handling most pistol cartridges and
a handful of rifle cartridges. The ac-
tion has found extreme success with
the Heckler & Koch G3 (7.62x51
NATO semi-automatic/select fire
rifle/carbine) and the MP5 (9x19mm
Parabellum semi-automatic/select fire
SMG). The roller delayed blowback
action should not be confused with
the short stroke, recoil-operated roller
lock-action, which utilizes a mechani-
cally locking breech design.
› Lever delayed – Like the roller delayed
action, the lever delayed action is ac-
curately named by means of resistance.
The lever delayed system relies on le-
verage from a lever to slow the cham-
ber’s opening. This may seem coun-
terintuitive because levers are typically
used to reduce the amount of force re-
quired to move something. This is true
if you are using a lever for its mechani-
cal advantage, but the lever can also be
used for mechanical disadvantage.
For example, a lever has a pivot point
(fulcrum) and two connected arms
(typically one long and one short).
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