Cookieman,
You will get better accuracy with the sabots and EXTENDED rifled choke tube. The short little flush rifled tube like in my sons 870 will impart some spin but the long tubes are way better.
True story: About 10 years ago, maybe a little more, I was at a Slug Shooting Weekend at popular Gun & Tackle. There were several Manufacturers Rep's there with all the slug guns they had to offer. The range is just outside the shop and shooting goes on all day. Browning had their A-Bolt 12ga with both the smooth bore with extended rifled tube and a fully rifled model. The Browning Rep told me that in their testing the rifled choke tube barrel consistently out performed the fully rifled barrel. This was a shock to me, because I never would have guessed that. He also said they were going to phase out the "more accurate" choke tube gun for the fully rifled gun because that is what the buying public wanted. How would you ever convince someone that the choke tube gun would actually shoot saboted ammo better than the rifled gun, short of shooting them in a side by side test? I'm sure that was the dilema that Browning had to go through too.
Now the A-Bolt shotgun is totally discontinued. :cry:
Just thought I would give you that first hand information from Brownings tests. Just make sure you get one of the EXTENDED rifled tubes that are designed for sabot slugs and I am sure you will be fine. I would not reccommend the flush rifled tube such as the 870 has unless you are shooting Brenneke Rifled Slugs, they shoot fine in my sons gun.