Around here, a 25 pound bag of shot costs $80.00. That's a bit rich & hard for casting into balls, when we paid $0.50 per pound for absolutely pure, Xray wall lead.
The harder lead is OK in a smoothbore, due to the normally undersized ball. I use a .595" ball in my .618" bore smoothie. If using hard lead, an even smaller ball would be likely needed
for the "tight" patch I use.