Sabot, rifle caliber projectile designed to move fast and travel farther and with a flatter trajectory. The plastic skirt obturates and fills the rifling grooves in the slug barrel to pick up its stabilizing spin and then drops away when the slug leaves the barrel.
Rifled slug can be shot in either but best in smooth bore. The rifling on the slug does nothing for stabilization and does not impart spin. The stabilization is designed into the slug with its light hollow base and solid heavy head. Think badminton bird. What the rifling does do is get swaged down as it travels through a choke at the end of the smooth bore barrel which may help center the shot for consistency on target. IC and IM chokes are good for that. Full chokes can be used but not recommended. Super full (turkey chokes) absolutely not used for slugs