The hammer on my Plains rifle has a cup on the striking area. It does not work well at all with musket caps. It will fire one out of three at best.
I use the finer T7 FFG, real black powder is not an option in this area. Nearest dealer for real black powder is nearly 40 miles away.
I found that by useing FFG T7, hot shot nipples & CCI mag capsI have very good results with both the Hawkins and Plains rifle.

Al