Inor
That would be the rifle I have -- Ruger's SR-556. It came on the market around 2009. While it MSRP for $2100+, I got mine for $1200 at a gun show a few years back.
From every review I've ever seen, it is one of the top rated gas-pistons. It is a little heavy because of the long Troy rail, and thick barrel, so when it is fitted out, it easily gets up over 10lbs. I have fitted mine out to meet my needs, or more appropriate, what I think my needs may be some day. This of course is NOT what others would necessarily want. For instance, guys like OSFG, want standard, no frills guns, so that they can pick them up at random on the battlefield. Well, I am too old to be going out on a battlefield. I have one shot at making a rifle superb -- and that is what I have done. Spent some money, but who's counting. LOL
As they fixed a problem with bolt carrier tilt about 4 years ago, the rifle is now flawless -- with one exception. No one cares for the OEM trigger, me included. But I have put that one behind me with this year's Christmas present -- a Geiselle. OMG, you just wouldn't believe how sweet it is. Makes me drool to go out and actually shoot some Zombies.
I am going to do a post on my gun in a day or so showing a whole bunch of pics that focus on each part that I have customized. It was a work-in-progress for several years.