I use a Weaver belt slot punch ,with a scrap piece of leather between the pounding board and the holster as this will keep the holster from getting marked up. We stitch around the slots when possible,after wet forming the holster I then take an awl,screwdriver,or dowl what ever is handy and rub the inside of the slots while still wet. Once dry I edge and sand but they are usually very smooth and uniform at this point.. Good Luck