I'll second the ghost on this one. Though I've got musket nipples for my inlines and two of my sidelocks, I've never found need for anything more than CCI #11 Magnum caps. Remington #11's seem just as good. Pyrodex RS or pellets go off just fine every time unless there's moisture or lube in the flash channel.
When I compared the #11's to the musket caps in my Black Diamond, I seemed to get slightly better accuracy with the #11's. Someone else wrote about finding the same thing (Toby Bridges? Sam Fadala?).
I've used the Pyrodex pellets and don't like them. They were usually OK for 3 or 4 shots from a clean barrel but I couldn't seem to settle into a consistently accurate load with them. The fouling gradually built up to where loading got difficult and accuracy went out the window. Loose RS, on the other hand, would usually reach a 'steady-state' fouling level with minimal between shot fussing. When this occurred, accuracy was quite good for as long as you wanted to shoot. I may try pellets again next year. I've learned alot here on the forum and I can see my swabbing/loading technique may have been the problem.
The pellets also seemed to kick alot harder for equivalent weights. But, if you can believe the numbers they put in the T/C inline manuals, this is because they're pushing the bullet out faster. Don't know how that works. ::
Bob