Someone correct me if I'm wrong, but I believe the Rifled slugs are for smooth bore barrels, and the rifling is on the slug. I agree, the slug boxes themselves for Sabot Slugs say "for rifled barrels only", so I'd only shoot the Sabots. I have an 870 20ga. with the 20" rifled slug barrel and shoot sabot slugs, and depending on the slug it'll be accurate out to 100 yards, that's the max I feel comfortable shooting with it. The best thing to do is sight in at 25, then 50 to get your scope on target (if shooting a scope) and shoot as many different slugs as you can find to find the best out of your gun. What shoots well out of my gun, might shoot like crap out of yours. I'm in that process now, finding slugs that shoot well out of the newest 20ga/slug barrel combo in my gun cabinet. My old standby, the Remington's didn't shoot well, so I've got about 6 different boxes of sabot slugs to try out at the range this weekend and see what fly's well.

My uncles, my father and myself have killed plenty of deer with a 20 ga. both smooth bore and slug barrels. It's a great gun, and even though I hunt PA and NY which are both rifle, I still sight in my slug guns and love hunting with them.