ar 15 upper opinions...

[RP88]

get the CMMG. It's a good start for a build. I would then replace their BCG with a milspec one.

 

[Z-Michigan]

I would then replace their BCG with a milspec one.

Replace just the bolt and save yourself $60 or so. The carrier may need to have the staking re-done but nothing else fails on a carrier.

 

[RP88]

CMMG's staking on their full-auto styled carriers is actually pretty snug and proper, but it still isn't made like a BCM carrier. But yes, definitely change out the bolt if you plan to run the gun hard.