Longbow,
If your barrel will accept tubes, get a rifled choke tube and see wat it does for you. I recently picked up a Carlson's extended rifled tube for my smoothbore 870. I tried my sabot loads through it with a variety of chokes but couldn't keep the balls on the paper at 50 yds. Best I could do was a 4" group at 25 yds. with the modified tube in place. With the rifled tube that same load gave me 2-1/2" to 3" groups at 50 yds, almost as good as my rifled barrel on my Mossberg 500. I was thrilled! The only ammo that grouped well in that gun was Remington Sluggers and Federal TruBalls, the full speed stuff. My sabot runs 1300 fps, so much easier to shoot! If your barrel's threaded, give it a try, you might be really happy !