Lapping uppers

[Tim K]

I don’t know, Bert. I like your thinking, but I’m not sure about a barrel extension “battering” the receiver. The two pieces are in intimate contact and under considerable compression due to the force of the barrel nut. The barrel extension doesn’t have any momentum to beat the end of the receiver because there’s no opportunity for it to move relative to it. I’ve taken apart several high mileage barrel/receivers that I’d lapped and I saw no evidence of peening.

I do it. I’m not convinced in the slightest that it provides any value, but I’m pretty certain it does no harm. To be fair, I glue my barrels in so there is even less chance for the extension to beat on the receiver.

[Osmosis]

Thanks for feedback and perspective.

My goal was two-fold. First I wanted to know that the barrel flange was seated against the flattest possible surface and when I saw the slight uneven surfaces on the face of the uppers I thought lapping would resolve that. If there is going to be some deformation from steel slamming against aluminum it seems that there will be less if the mating surfaces are as flat as I can make it, as opposed to small concentric ridges. Secondly I want to have the sights as close to centered once I sight it in because if they are off to one side I will be forever haunted by the thought that I could have lapped the upper and didn't. (This last point is probably an OCD thing)

BTW: I am planning on bedding the barrels with some loctite green goo so they will be pretty close to a single unit when all said and done.

Once I get the first one assembled and sighted in (an RTB 22lr) I will update the results - mid summer probably.