A logical question. I've always loaded my Brown Bess with paper cartridges rather than carrying separate powder, patch and ball. Use a small enough ball (.715) that I can just start them with my thumb even after a dozen shots.
I will often carry my Pedersoli-made Harpers Ferry pistol at the same time, 58 caliber with a rifled bore. It works quite well with a 500gr minie ball and 35gr FFFg. I've done some experimentation making up paper cartridges in that combination but they just haven't worked out all that well. Using a .562 round ball however they are just smaller versions of the same cartridge that I make up for the Brown Bess. 3 wraps of recycled news print does not make the most effective patch for a rifled bore though. Reaming out the rifling would pretty much solve that problem....
That's the why.
A couple of people have suggested that since this barrel normally has 3 fairly shallow grooves in a pretty slow twist that I could probably just ignore them and pretend the barrel is a smoothbore in the first place.
Will know for sure when I get out to a range in a week or two for some serious practice. If it will reliable hit a gallon milk jug at say 10 or 15 paces then I probably couldn't ask for much more.
