CCI made the muzzleloading world a lot brighter in 1975 when they introduced their percussion caps.
Why? They were non-mercuric, non-corrosive, and darned reliable.
When using any percussion caps for reenactment or demonstration shooting without a powder charge or bullet, only use nipples with a large internal diameter. Standard nipples intended for normal loads can clog when fired repeatedly without a powder charge, potentially causing the cap to fragment. We recommend a minimum internal diameter of 0.050 inch for nipples used without powder charges and bullets.
#10 cap . For revolvers with smaller nipples