Got a question on a forum this morning, and I thought I'd share it, and my answer, here.
"I'm thinking about buying a piston AR, specifically the Ruger 556. Anyone know anything about them?"
Well, I haven't shot one, but I got a good chance to handle it; plus I got about a 20 minute interview with the chief designer, and the head of the production line on the project; at the NRA convention earlier this year (unfortunately my recorder had a mic malf, and I could barely hear them over the crowd noise on the recording, so I couldn't run a transcript).
My take, is that it's pretty much like every other piston AR, but less expensive. They're sourcing all their standard parts, from the standard manufacturers; they took the time to get the non-standard engineering right; and it looks well made, to a higher standard of fit and finish than most other Rugers.
I also got to talk with Michael Bane a while about the gun. He had taken it out and tested it a couple days earlier; and they put 1500 rounds through it without a malf. It shot well, but like all piston AR's the recoil felt different, and it wasn't QUITE as accurate as a conventional AR would be (a couple percentage points difference).
If you want a piston AR, and don't feel like paying Leitner-Weise (or later this year HK) their rather significant premium, then it should be a good choice; but as was said, wait a couple months and see how they shakeout in the field. Ruger has had some issues with early production run guns lately and it would be wise to let other people experience those problems before you jump in.
Two years ago I would have also thrown POF into the mix, but reports are that they are having some production issues right now, and may be having some cracking and failures in action. Until those settle out, I'd stay away.
POF is actually local to me, and I know a couple of the POF guys read my blog on occaison, so if y'all feel like commenting, go for it. I'd love to hear that you're sorted out.
Of course there's a larger question you have to ask: Are you sure you want to pay the premium at all for a piston AR?
No evidence has shown that a piston AR is any more reliable than a conventional AR of equivalent quality, fit, and finish. The only real improvement is that they are easier to detail clean, and you don't necessarily have to do it as often.
You all know how I feel about cleaning a service rifle. You shoot, you clean. You move, you clean. You breath funny, you clean. So increased cleaning intervals don't mean much to me; but there is a slight advantage there in being easier to clean.
Lord knows I would be happy to have a rifle where I can get a pipe cleaner through the gas port without risking getting something jammed in the gas tube an buggering the whole thing up; and if I never have to clean carbon out of a gas key or bolt recess again, that would be great.
On the minus side, they are much more expensive, considerably more mechanically complex (which is a REDUCTION in reliability. More moving parts to fail), and somewhat less inherently accurate (more moving parts means more reciprocating mass, more vibrations, more disturbances etc...)...
Oh and they're all a bit heavier than an equivalent conventional AR, and most of them get a LOT hotter under the handguards a lot faster (and don't dissipate that heat as fast) in rapid fire than conventional ARs do (hot enough to induce failures in some cases).
'Course I've had a gas tube disintegrate on me before as well, so it's not like conventional AR's are without fault in that department.
Actually, there is one other point in favor of the piston systems: If they have an adjustable gas regulator, you can adjust the timing better for your conditions and configurations (direct impingement systems can sue adjustable gas regulators as well, but to lesser effect).
Because of that, they'll tend to function better in extremely dusty environments, or with extremely dirty or inconsistent ammo; and you can adjust to compensate for barrel length, your load (high pressure 77gr vs subsonic loads for suppressors for example), or if you're going to use a suppressor (suppressors foul gas systems very easily, and often do not cycle gas actions reliably).
That point right there could make them worth it all by themselves.
Unfortunately, not all piston ARs HAVE an adjustable gas system, and some of those that do (including the SR-556) have it as "open, 50%, closed"; which is still an advantage, but less of one than a fully adjustable system would be.
Of course, in a field rifle, you don't want something fiddly, or prone to backing out, or difficult to adjust in the dark, with gloves on... so it's a tradeoff. On balance, it's still useful to have.
Overall, I'd call the SR-556 a good rifle buy, once it's been in the market for a while, and the kinks have been worked out. Oh and I'd like to see more options and more configurations like other AR makers offer. This being Ruger though, I think they may be going for simplicity of production more than tactical Barbie.
At the $1500 to $1700 price point the SR-556 is at (or will be at once full production capacity is reached, initial demand lessens, and the Obama hoarding is completely over), I think it's probably worth buying over a conventional AR of similar configuration. Realistically, you're only paying, at most, a $400 premium (and generally, much less than that) over a similarly configured conventional AR, when you count the rail system, sights etc...
As far as the other piston rifles go, I just think they're too expensive for what you're getting. LWRC, POF, and HK all make very good rifles (yes, really, even with the current problems the POF's have in general been very good); but to me, not good enough to justify their premium pricing (all $2000 or more, fully equipped), now that a lower cost alternative is available.
Honestly, if I'm going to spend LWRC kind of money, I would rather spend it on a Wilson or a Noveske, or something similar; and get a much better conventional AR.