Receivers for Top Tier barrels

[Mustangfreek]

I’ve found that Most billet uppers are tighter fit then std forged uppers..

That is in my experience in dozens of various uppers and configurations.

I know Lap, goo, and shim all my forged uppers, regardless of who their from, but haven’t used a bcm upper. If I was I’d look at the newer one, Mk something or another, with more meat up front.