I just put together another AR and the BCG doesn;t fit snug in the upper reciever. is that an issue?
its going to be difficult to convey to us just how loose the fit is… but your carrier doesn’t need to be “snug” in the receiver- it just needs to be tight enough that it reciprocates smoothly. some combinations can be tighter than others, but most standard “milspec” carrier/receiver fits have some play.
what brand carrier and receiver?