Anybody here have a Ruger SR 556...?

[9Ball]

....and I would be interested in hearing good and bad points for the piston system as opposed to the gas tube.

thanks...

[The Anvil]

Drawbacks? Additional moving parts. That's about it.

Advantages? Less heat acting on the bolt, gun stays cooler. No fouling gasses make their way to the bolt as opposed to direct impingement and all of the drabacks that go with that.

I haven't shot Ruger's version but I have shot the Sig version in 6.8. I liked it a lot. Personally, if I relied on a weapon for my life and I had the choice I'd opt for the piston driven bolt key as opposed to the traditional DI system. But that's just me.

[Jess from VA]

Some reading:

http://thefiringline.com/forums/showthread.php?t=291416

http://survivalcache.com/part-3-best-survival-carbine-ar-style-rifle-bug-out-rifle/

http://www.tacticalgearmag.com/page/ar15-piston-pros-cons

If you are looking for a complete rifle, an M4 variant 16" bbl, mil spec, of good quality, for a good price, it is hard to beat the Stag Arms Model 8  (and they have lefties if you need one).  It's what I got.  Carrier tilt has not been a problem with them.   

http://www.stagarms.com/product_info.php?cPath=13_22&products_id=321

Besides an EOTech 552 holosight, grips, forend, buttstock, forward grip, I got a roller cam pin for added reliability.
http://www.pof-usa.com/parts/arparts.htm

[The Anvil]

I like that roller cam pin. I might have to get one of those.

[Jess from VA]

I like that roller cam pin. I might have to get one of those.

Besides carrier tilt, some piston ARs have had the bolt carrier (and/or cam pin) scratch/scrape/shave metal off the inside of the receiver from shooting (the piston being a bit more violent a mechanical action than the gas system).  I believe this is why the roller pin was developed.  If you have a gas impingement AR which has been fired some, and pull the bolt carrier and inspect in there with a light, and there are no significant shiny scrape marks anywhere, you probably do not need the roller cam pin at all.  In doing my homework for the Stag #8, I found some had shaved some metal (and others had not), so I put the roller pin in right away when new.

FYI, someone else also makes a Teflon coated (ordinary) cam pin which is supposed to be about as good as the roller pin in solving such problem..... for cheaper.