You can use all slugs in a smooth bore AR12. It is said rifling on slug or barrel increases accuracy. Been shooting slugs for 40 years, rifled, sabot, regular slugs, smooth barrel, rifled barrel. Very little difference.

John, you will have no issue firing slugs through an AR12. Without rifling, you will get better accuracy using "Foster" Type Slugs in the smooth bore. I heavily use/favor the Benneke K.O. Slug load.

Yes you can shoot slugs in it with no issues