This discussion reminds me of the old explorers statement, “ have lost all sense of direction we were able to double our speed”. The ball does not need to be near bore size. In fact just the opposite is the case. Shooting a bare ball depends on the ball riding in a cone of hot gas, that keeps the ball from contacting the barrel, and imparting spin, I shoot a .595 in my old trade gun that has a .625 bore, and a .590 ball in my old North Star that has a .620 bore. A ball that is too big reduces the size of the cushioning gas, and increases the possibility of barrel contact. The increased powder charge insures the existence of the cone of gas, and makes sure there is enough to allow the ball to clear the barrel. As the ball loses velocity it will start to drift, but without patches, wads, and who knows what else, the pressure is low, as is the recoil. Tow, or some old wool blanket, will be blown out ahead of the ball, and will not deflect it.
Hungry Horse