Page 110 - FAT 105 4.17 MOODLE

Figure 32b : Long stroke piston system.

Squad Automatic Weapon (SAW) all During discharge, high pressure gas acts
use a long stroke piston system. There upon the piston, driving it rearward.
are even variants of the AR-15 (which Depending on the specific model, the
uses a direct impingement system) from piston may act upon the carrier directly
Primary Weapon Systems (PWS) that or against an operating rod that acts
utilize a long stroke piston action. upon the carrier. The piston will only
move a very short distance, but will
• Short Stroke Piston – The short stroke
impact the carrier/operating rod with
piston system operates in a similar man-
enough force to create sufficient mo-
ner to the long stroke system with a
mentum in the bolt/carrier to overcome
few minor exceptions. Unlike the long
the resistance of the action/recoil spring.
stroke system, where the piston is fairly
Often the piston and operating rod are
long and travels the length of the ac-
spring-loaded, which will push them
tion’s stroke, the short stroke system uses
back into their resting position until the
a shorter piston that is a separate piece
firearm is discharged again.
than the carrier. When the system cycles,
the piston only moves a small distance Although the short stroke piston system
compared to the bolt/carrier, which trav- may seem more complicated than the
els the full length of the cycle’s stroke. long stroke system (because of the in-
creased amount of parts), the short stroke
The short stroke piston system is also
system has the advantage of being lighter
known as the “tappet” system. A tap-
than the long stroke system. Because the
pet is a mechanism that imparts a linear
piston is a separate piece than the car-
motion to another component within a
rier, the carrier assembly can be lighter,
machine. In the case of the short stroke
as it does not require a provision for the
piston system, the piston is often referred
piston. This means the short recoil system
to as a tappet. Depending on make and
requires less energy to cycle the action,
model, there may also be an “operating
which translates to less recoil. The design
rod” that lives between the piston and
of the system has a built-in flaw in the
the bolt carrier.
form of the operating rod, which is often
fairly thin and prone to bending/breaking.

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