+1 to all of the above.
explain to me what the bore butter is being used for, I'm kinda old-timey & have always passed by the stuff w/o paying attention. As a bullet lube it shouldn't effect the load, but maybe it has some other purpose?
If it, or any other substance beside BP is in the barrel then u got problems waiting to rise.
If i have oiled my barrel i make sure my first shot or two is nuthin but BP, no bullet at all, just to burn-out any oil (or butter??). Then I may run a patch down, but more likely just a bullet. I use patched balls in my .45, saboted FMJ's in my .50, and pure lead minnies (how can they call a 500gr bullet a minnie?) lubed w/Crisco in my .58 - I find any one of these scrubs-away the fouling & sets me up for a nice shot thereafter.
BUT, I would avoid putting powder down the nipple, all it will accomplish is a slower bang, or even a hang-fire. If that seems to work for ya, then i'd suggest skipping the nipple-pick & going right for the wrench... you may need to check & see if there's a good place for the fire to enter the bore. Sounds like it might be carboned-up as some suggested, but might even be that the hole needs to be opened-up a bit.
I'm anxious to hear how this ends-up. & hopeful for pictures!! I do like a caplock!