Home Forums Hunting & Shooting AR and Tactical Rifles Tac 20 build (pic heavy)

Before I started on the barrel, I figured I'd check bolt lug contact in the barrel extension, and lap the face of the upper receiver.

Wrong bolt in this pic (that's a Grendel bolt), but you can see how the bolt and barrel extension lugs interface in an assembled upper:


Bolt lug engagement was adequate but not ideal. You can see less contact on some of the lugs; this was a result of the receiver face being slightly out of square.


My lapping fixture in the receiver. The fixture is a Brownells receiver extension, I bored out and pressed on a large nut, then turned the face square for lapping.


Where the lapping action happens:


Results of the first pass are pretty good. Could stop there but might as well take it a little further. We're looking for bright white lapped area all the way around, or close to it:


I'm calling this done. Looks like a low spot at 3:00 on the face of this receiver, but we have enough contact everywhere else that it won't matter: