I lap all of my rifles. All have Nightforce scopes, Nightforce or IOR rings, and full lenght (Picatinny or similar) mounting rails. I figure after spending so much money on the action, scope rings, and scope you want to apply a similar amount of accuracy and fit between the scope and the rest of the rifle. I use the lapping tool & compound that Sinclairr International sells. My process is as described by Phorwath above. Sometimes very little lapping is required, other times it takes a little more; but usually its takes no more than 10 minutes. If I remove the scope rings from the rifle then I always re-lap when they go back on; however it is always a very good idea if the rings are going back on the same rifle you record their orientation so they go back in the same order, direction, and position on the rail (if possible) to minimise the lapping required! Applying this process for example when an action is re-barreled and not changing the scope zero I have found the point of impact may hardly change at all (e.g. within 1 MOA!! - or maybe i just got lucky).