Leather Punch. I highly reccomend one.
I own one of these, blades on it werent sharp (nor were the replacement blades I got with it), but I work with metal allot and managed to get em razor sharp. Worked like a charm after that.
I'm just going to assume you (or anyone reading this wondering the same thing) don't have the means to sharpen the blades, so heres a method everyone can use:
as soon as i noticed i put something under it nd stopped the problem...
mmy jacket has a little over 900 studs in it. i used a flathead screwdriver and an 8 pound weight and looooots of weed lol. weed for the patience