The game laws in Iowa did not permit the use of sabots. Maybe they're more consistent. I also had (still have, actually) a Rem 870 with 20" smoothbore barrel and rifled choke. With that combination I would not have attempted shots beyond 100 yards under ANY circumstances. Just not precise enough, despite the fact that I spent a lot of time at the range and tried many different loads.
Are you using a fully-rifled barell? What kind of gun? Count yourself either very lucky or an extraordinarily gifted shot if you can keep slugs within 5" at 200 yards! No one I've ever known could do that with their guns.