Bear in mind that cast balls will have a flat spot for the sprue, and some may have a slight nub at the gate where the molten lead was poured into the ball mold. Can't get much more of an out of round than that. The sprue is compensated for by loading with the sprue up and centered. Weigh the balls to have the same weight ball used for each shot and to eliminate the cavity that sometimes is drawn into the ball as the molten lead cools. Some will roll the freshly cast balls between two plates to smooth out the sprue. Some just take care to always load with the sprue up and centered in the bore, relying on the concave loading jag to smooth the sprue. And of course, with soft lead there is the factor of obturation as the ball is slightly compressed on firing to conform to the barrel within the patch. Since these balls are being fired in a smooth bored barrel, I don't think that the slight out-of-roundness will have significant effect.