Be aware that there are real full power musket caps and there are musket caps made for "reenactment". You do not want the reenactment caps, they will not reliably ignite any type of powder.
How it got this way:
A Mensa candidate lost an eye when a musket cap fragmented during a reenactment: Yep, the guy was not wearing glasses. Our "victim" sued CCI who fixed the problem by making very weak musket caps for "reenactment". RWS soon followed suit; they changed their 1081 caps. The new RWS 1081 caps are no good either.
You want the RWS 1218 six winged musket caps, the old CCI four winged caps or the old RWS 1081 caps.