From my limited knowlege of slugs;
Rifled slugs (Foster or Brenekke type) are for smooth bore or non-rifled barrels (or rifled chokes).
Sabot style slugs are for rifled barrels or rifled choke tubes.
From what I've read and been told (I have not experienced it first hand) a sabot style in a smoothbore, will give you about 50 yards with reasonable accuracy. Beyond that, it goes downhill fast. I reason it like a football. In a spiral, it goes farther and more accurate, then a football thrown without a spiral.