imho, when having a choke bore barrel the cloth patched undersized round ball is the only chance to be safe in the long run.using a shot cup as sabot is another way but not the best with black powder because it burns to hot for the plastic.
I cant imagine that ball and patch leave each other before this combination leave the muzzle and the patch fly away by the air drag. the pressure of the gas move the patch like it move the ball in front.