I think Brownells sells lapping kits. A lap is essentially a cylinder of the correct diameter with some grooves to hold the abrasive compound. A handle is mounted at 90 degrees.
The Remington 700 is perhaps the most widely used action for precision rifles. The receivers are mass produced, and heat treated after machining. A bit of warpage can occur. A 40X has some machining done after heat treatment to reduce this. Take a steel straight edge and apply it to the bottom of the receiver; you may be able to see curvature; or mount the receiver on a mandrel and turn it over on centres. If a stock with a machined bedding block is used, the receiver may not fit properly, and some bedding compound may be necessary. Or the receiver may be mounted on a mandrel, and the bottom trued up. The first time I did this, I was amazed at how much material was removed to true up the bottom of the receiver. Now if the bottom of the receiver is warped, the top will be as well. If the top of the receiver isn't true, torquing down a mount is going to stress the mount, receiver, or both. Lapping the rings should reduce stress on the scope. I suppose that ideally the mount and receiver should be fitted to each other. This is why I like the Burris signature rings. Even if the receiver and/or base and/or rings are misaligned, the scope can still be mounted without it being stressed. Kelbley benchrest rings use metal inserts to allow the scope to be floated. The serious precision actions - and there are many - are machined so that the barrel, bolt, and receiver are aligned.
