Here's a percussion capper I made as a prize for our monthly postal shoot over on americanlongrifles.org. It is made from 10 -12 oz backed with 8 to 10 oz. The holes along the edge were drilled on a drill press using a #13 drill bit (IIRC). These are super cappers for single shot rifle or pistol, they hang upside down so don't get wet and don't lose caps. Simply slip the cap over the nipple, and pull the capper away sideways. The cap comes free through the slit in the capper's edge.