Monday, April 20, 2009
Farnam:Gas Piston AR's Unreliable (?)...
From John Farnam:
Gas-piston Stoner Rifles:
I just completed an Urban Rifle Course in UT. Students brought the
usual assortment of AR-15s and Kalashnikovs. We also had one RA/XCR
(mine) and one DSA/FAL. All ran fine for the duration, except for one
of the AR-15s, which was a gas-piston model. All the other ARs were
conventional Stoner System (pressurized receiver) models, and all
experienced no more than the usual number of hiccups.
However, the one gas-piston ARs displayed many unscheduled
interruptions, mostly failures to eject. We all made a mental note that
this is not a rifle any of us would want!
Unhappily, this experience has been typical at our UR Courses. As a
rule, gas-piston ARs do not hold up nearly as well as conventional ARs.
To add insult to injury, gas-piston ARs are a good deal more expensive
than are standard models!
It strikes me that, in their enthusiasm to maintain the classic AR-15
profile, designers attempting to equip this rifle with a gas-piston have
produced both a piston and op-rod that are tiny when compared with those
found on the XCR, SIG/556, and other military rifles in the same 223
caliber. Apparently, a gas-piston system that small is below the
reliability threshold, because we can't seem to keep them running
The original Stoner System (pressurized receiver) has had a
disappointing tenure. Compared with gas-piston systems, like the
Kalashnikov, it has been excessively maintenance-dependant, because so
much garbage ends up in the receiver. Gas-piston rifles don't get
nearly as dirty, nearly as fast.
However, in my opinion, gas-pistons and op-rods must be substantial,
even on rifles chambered for 223. Tiny parts and tiny systems do not
reliable rifles make!
(John clearly has his brand preferences. It's not clear if they have
influenced this report.)