My doctor, wife (and arthritic shoulders) finally convinced me to give up my more robust rifles... anything with more push than a .223 leaves me unable to use my right arm, for much more than lifting a fork, for a time after that, so just before Christmas I went horse-trading and came home with this: This one is a SIG 556 ER. 16" barrel, gas piston action, generally over-priced, but I found this one with a good price and made a good trade. It's 5.56 of course, uses USGI M16 magazines, but came with two Sig poly mags that clip together. Standard AR butt-stock compatible, the collapsible on it now is OK. The hand-guards have lots of rails, if you like that, but I think it'll need some standard Sig 551 guards (the rifle this one is based on). Good trigger, with folding iron sights, the cheapy dot sight was part of the deal, along with the factory case, and papers.