Ive been using the Siam mod carto punch for a while, works fine for a long time , then it gets real dull. Without have a specialized tool for sharpening Ive tried sand paper, and a dremmel to sharpen it, but I cant seem to get a real even diameter and perfect point. I have since discovered a wonderful tool, that barely leaves a dent, just slight. I got it at VIP electronic cigarette
Aluminium Cartomizer Punch V4 - Cartomizers/Tanks - Accessories
They have excellent service and are the originators of the aluminum carto punch. It has a window to see how deep the hole is going, I twists like butter, so be careful sometimes its easy to make the hole too deep cause its so effortless. Doenst crimp the carto so it doesnt cause it to pinch and affect the flow. It was expensive but the screw is a Cobalt Tip so it will keep its point longer and they do sell replacements.
I am glad I found VIP.