I am assuming by "Slug Barrel" you mean a rifled barrel. If that is the case you sure can shoot shot loads in it. You probably will not be able hit much with it though, the rifling spins the shot cup and flings the shot into a very wide pattern as soon as it leaves the barrel. That is why the 45/410 Contender barrels have a choke with straight rifling, it stops the shot from spinning.