Technically speaking no one makes an AR15 but Colt. But that's splitting hairs. I was recently told by a local gun store that you cannot mix uppers and lowers when it comes to RRA stuff. I know this to not be true. I built a Spike's lower/RRA upper a couple years ago and it turned out fine.
My latest build, All Rock River, just waiting on the barrel. Only problem is, it is on indefinite back order. Placed order in July, no barrel in sight.
