I used a Black & Decker Mouse detail sander. It is like hand sanding without the fatigue.
Note that according to Ruger Inc., you will be voiding your "warranty." IOW, they will charge you for work on such a cosmetically changed revolver presumably because you are exposing them to future lawsuits from a subsequent buyer who didn't READ THE MANUAL AVAILABLE FROM STURM, RUGER & CO., SOUTHPORT CONN.
I did it and could care less if I have avoided Ruger's repair service for my GP that always works.