As mentioned, it's tough to screw into a rb, then it will tend to expand. One doesn't get much purchase into the ball. This may pull out of the ball when trying to drag it up the bore, especially if the bore is fouled, hot and dry from shooting. The saving grace is whatever lube is on the patch. Also, the conditions mentioned can be neutralized by dribbling some water down the bore...makes it much easier for the prb to be pulled up.
Having said that, I prefer pulling the nipple and installing some BP in there (rollingb first gave me that advice years ago). And you can use whatever granulation of BP you have, doesn't need to be priming grade.