I use a drill press and drill bit that's about 1/16" smaller than the hole. Tear a 2-3" ribbon of 400 Emery paper, attach to bit with thin painter's edge tape (the super-thin blue stuff), and spiral around the bit. Lube with wd-40, ATF, or water. A thousandth is easy, in fact that's about what gets removed during a "standard procedure" Lee push-through polishing operation. I like to let the die spin slowly as I'm lapping to help keep it round, and bob the die up and down to get a cross-hatch pattern inside.