Im building up a ar15 from a S&W-M&P 15 stripped lower. I'm going to get a 2-stage RRA lower Rec. kit ,to do the lower.But I'm trying to decide what assembled upper to go with JT,MA,Model1,RRA,or,DPMS. I'm looking for a varm. or a bull barrel,but I'm not sure who produces a good quality piece for my build. Has anyone had issues with any of these companies