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.