If it is the flush (not extended) rifled choke tube? My son has the 20" barrel for his 870, I.C. choke and flush rifled. We have never shot the I.C. tube because the rifled tube is so accurate with the old Rottweil Brenneke's and the Winchester Foster's (1600 fps). There is some choke in the rifled tube too. We tried some of the cheap WOLF slugs, they shot good at 50 yards, but were all over the place at 100. I think they are too slow, and lost stabilization somewhere between 50 and 100.
He uses his barrel for turkey also, the Remington Super Full extended tube does a fine job.
If you want to shoot sabots, get the Remington extended rifled tube. We have never shot saboted slugs through the flush mount, so I can't tell you how well it will stabilize sabots.