I tried a few different slugs; Brenneke Gold 3", Challenger, Remington 3" Slugger, Federal Premium Sabot, Federal Premium Nosler Partition Sabot, and regular Foster type Federal 3". I don't recall grain/oz. at the moment nor group size, as shots would be at wounded bears which would be hurried and close range. I just wanted to find something that didn't spray uncontrollably. That said, I don't recall any of my grouping being like caramel's in the post above, but I was shooting offhand standing.
I had the factory modified tube and a Carlson's rifled tube. I got the best accuracy with Challengers out of the rifled tube and the Brenneke's out of the modified. The Challenger's were a close second out of the modified as well, so I went with them. This was at 50 yards, but I suspect 100 yards would yield very similar results.
Strangely enough, the Brenneke's I have state "For rifled barrels only" on the box, though they look like the standard Brenneke's I've had before, though those were 2 3/4".
The rifled tube shot the sabot slugs as poorly as a smoothbore, so I think they're really a gimmick, unless you get lucky and can improve upon a certain type of slug meant for smoothbores, like the Challenger in my case.
Bottom line; stay away from saboted slugs unless you have a fully rifled barrel. I pretty much knew this beforehand, but it was more of an experiment as I had a bunch of ammo and no longer own a rifled bbl. shotgun.