What you could do to feel a little more comfortable is upgrade to a mustket nipple/cap. I did that on my first Mler that wasnt very reliable with #11's. You can even buy these little pink rubber slips that go over a #11 cap, put that on the 11 nipple and a musket cap slides over it snuggly. Its works like a charm and you'll never have to change nipples. Its worth a shot.

I dont see how putting 10-20 grains of real BP down the bore would be better seeing how BP is a lot more sensitive to humidity and attracts it. I'd just try my lil tip and leave it loaded for a few days and see how it goes off when you're ready.
My dad went home empty lastyear when his cabelas hawken misfired due to no powder being in the nipple drum area. That was a disapointment.