I have "Comet lapped" some of my molds to make them release better. I cast a bullet and cut the sprew. Keeping the mold closed I drill a small hole in the center of the bullet base about 1/3 of the length of the bullet. I screw a hex head sheet metal screw into the hole until tight and remove the bullet (now the lap). I now make a Comet cleanser paste with water and apply it to the lap. Using a drill with a hex driver to fit the screw head, I put the lap back into the mold and turn it with the drill, holding the mold tightly together. Reverse directions several times (lap perhaps 10 minutes, forward and backward). Using Comet removes very little if any metal from the mold, so bullet dimensions don't change. Clean the mold and cast some bullets. On some molds I have used this same method but used fine valve grinding/lapping compound to clean up and open up the cavity some. Go slow and check often...