Seems to me the carbon in the breech plug will be more of a variable, than the soot in the barrel. Keeping the flame channel clean with a hand spun drill will make for uniformity. If you insist on messing with the barrel, perhaps a dry patch would be as good as any. When i shoot BH, i like it when about 5 shots have gone through the barrel, because, after that, it seems like things more or less stabilize.