Squaring & Lapping the Upper Face

[GMinor]

Gminor - with a setup such as yours, I would be hard pressed (no pun intended) to imagine the receiver face could cause any misalignments, since your fit is so snug. I know of at least one billet upper where the mfgr recommends freezing the barrel & extension, and heating the upper, prior to installation. Now, THAT sounds like a tight fit, to me.

It came to that, but my barrel wouldn't fit in the freezer. So I went the next best route, bigger hammer and that oil you get with a geissele trigger (that stuff creeps like crazy!).