There is a law of diminishing returns in shooting as in just about everything else.  Lapping is more about more evenly distributing the force/contact area of rings to scope to eliminate binding.  After seeing the improvement from action bedding/free floating to eliminate binding within the gun, I figured lapping probably couldn't subtract from accuracy.  But after bedding, using higher QA handloads, some trigger work...there's not much noticeable room for lapping to work with for chasing a smaller group.