If it says "sabot" anywhere on the box, avoid it. Those are for rifled barrels.
Rifled slugs are for non-rifled barrels (smoothbore).
If you look and the end of the loaded round and see unjacketed lead, either round nosed or hollow pointed, you should be good to go. If you see something that looks copper plated or jacketed, you are probably looking at a sabot slug that will not shoot accurately out of a smoothbore beyond about 10-15 yards.