I've started firing lead shot from a rifled long barrel, experimenting with different loads to improve (maybe!) the pattern. I'm not an expert, but I'm not worried about damaging the rifling with lead shot, since lead is a LOT softer than steel. Maybe when I've shot 1000 rounds I'd see some slight damage, I don't know, but I don't think there would be any more wear than shooting round balls.
But then again, as I said, I'm no expert :surrender: , so someone may have better information.