Eldequello - I think you are right on the money in you supposition that patched round balls and plastic sabots will have a minimal effect on barrel wear. The only thing I have wondered is that black powder residue seems to be a lot more abrasive than other powder residue. I could imagine this abrasive effect, over time, wearing the rifling down. As you probably know, one of the standard methods of cutting hard steel is to use an abrasive compoundand apply it toa softer metal (like brass or aluminum) first. This will cut the hard steel better than applying the abrasive to hard steel lap. Something like this probably goes on with the lead bullets going down the a bore coated with black powder residue. (I know it happens with aluminum cleaning rods coated with powder residue). Bet it would take two lifetimes, though. And those of use who swab between shots might not get much wear of this type either.