Hope I don't get slapped for this, but if you are going to spend hard earned money on an ar, build a lower and buy a Daniel Defense upper or BCM and get either of those in the mid length gas system. Those are both "top shelf" uppers which are considered beyond mil spec and will last you many thousands of rounds. CMMG in my opinion is not of very high quality. I don't mind using their lower parrts kits just like DPMS but would never buy a DPMS upper.