You can't use rifled slugs in a rifled barrel because the rifling on the slug will chew up the rifling on the barrel, and vice versa. This will cause excessive wear on the gun, and eventually make it unsafe to operate, and it will severly deminish the accuracy on the rifled slug, and the accuracy of the barrel. You should be able to find some smooth slugs that are made for rifled barrels, not just the sabots, because you're right, sabots are expensive. But remember, bigger hole doesn't necesarrily mean more damage. Most sabots are made for hunting, and because it's a lighter round it's moving faster. A sabot will damage about as much as a slug because it's moving faster, but it's lighter. The payoff for the sabot is that you get better range and better accuracy because it's moving faster.