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
satisfactorily.

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

(John clearly has his brand preferences. It's not clear if they have
influenced this report.)