Most of my guns have had the "thumb smoothing" treatment. Actually, I start off using a conical plumb bob. Being sharp pointed it will fit about any caliber. I start off with coarse sandpaper then go to a bit finer grade. This gets the heavy work done evenly. The last step is with emory cloth and a thumb. Yes, it does take a while but I'm congenitally slow, anyway. As far as I can tell they look quite even.