Recommended barrels for new build

[jkingrph]

am, tell me more about lapping the upper and bedding the the extension. How do you accomplish this?

It's been a few years, but Brownell's had a receiver lapping tool, that squared the receiver face that mates to the barrel to the bolt carrier raceway so the bolt should be square to the barrel extension and barrel You insert it , apply a little lapping or automotive valve grinding compound and turn it. check frequently until all the high spots are removed and you have a uniform polished receiver face.