Some brands of primers and percussion caps are a lot "hotter" than others. When I used to compete seriously with round ball m/l rifles I would test percussion caps by capping the nipple of an unloaded rifle, standing it vertically at the loading bench, placing a dime on the muzzle and pulling the trigger and noticing how high the dime went. It was amazing how much difference there was in brands. They had to equal or beat RWS brand to impress me.
When I was a child I had a "Davy Crockett" Kentucky that used rollcaps. It came with cork balls that you loaded down the barrel against the breech. Those minute roll caps would send that cork ball really flying out the barrel!
