I drank the piston cool-aid and purchased the SR-556. Accuracy is about 1moa with good ammo. Certainly more accurate than other chrome lined ARs I've shot. It has all that one could want out of the box and has a nice EBR feel to it.
I get a large feeling of 'meh' over not being able to break it down further like the SIG. The op-rod is pretty simple and really doesn't need anything maintenance wise. The piston and regulator will give you some grief if you let it foul up. And in true Ruger fashion, it could be easier to open up and put back together. Mine has a little bit of carrier tilt and I'm thinking a Seth Harness anti-tilt buffer is on the horizon. The chamber is tight and doesn't like wolf. No biggie for me as I have a nice stash of good brass for it. The hogue grip is nice but does nothing to remove that teeny tiny feel that AR grips have. The trigger is good for AR standards but still nothing to jump up and down over.
I like it and will keep it however it has more cons than pros. It's heavy. Piston conversions (the Ruger is a conversion and not some redesign) have inherent problems with carrier tilt, cam pin drag, and some suggest uneven lock/unlock of the bolt. The regulator can cause a hassle to remove if carbon is left to build up. And once you understand the AR a little better, spotlessly clean ARs are a bit of a waste of time.
Some words on maintaining an AR. The DI AR is *simple*. Unless your shtf scenario includes some Dune like environment with lots of sand or you plan on using antique ammo with corrosive attributes, put away the notions of keeping it clean. My zen moment with DI carbines is when I gave up keeping the bolt/carrier/upper receiver clean and moved on to accepting a sloppy soup of thick axle grease along with a few drops of motor oil to thin the grease out a little. Run a bore snake through the barrel, ensure the chamber and bolt face is clean, call it a day. Every 500 rounds or so, wipe everything off with paper towel, remove any excess carbon build up from gas chamber and the back of the bolt, re-grease/oil. The so-called POS Bushmaster I sold to fund the Ruger functioned like, like a well oiled machine. :wink:
If you can get past having a gun that is not spotlessly clean in your safe, get a DI S&W M&P15 or better and call it a day.