Musket caps could probably light a cigar at the other end of barrel. One thing to keep in mind with black powder, you don't have to blow it up, you only have to ignite it... and being an inline, a #11 cap will do just fine. In fact, a #11 cap will serve you better with an inline in the elements, if it is exposed like it is on my Whites. The only thing musket caps have going for them is that they at least are easy to remove and don't generally wind up in pieces.
Musket caps also will clear out any oil or debris left in the chamber if you clear your muzzleloader (like you should) before loading. I prefer musket caps myself, but #11's have nothing to be shy of in an inline.
Aloha...