Again, Jerry V is giving you excellent suggestions! The danger increases significantly with a doublegun-both in loading and firing.
I'm not familiar with your piece or any production muzzleloader, but your barrels are most probably cyl bore, and you'll not get the range that you are used to with modern pieces. You mention corrosion in the bores: is this heavy pitting or does it look light? You may want to scrub the bores with 0000 steel wool and lapping compound to take out as much as possible. Loading will be improved. I use Circle Fly wads and lube with bear oil or deer tallow. Olive oil will also work very well, and all three of these lubes are "Period Correct" if that's important to you.
