The H&R website says this about their ultragon rifling.
Ultragon is a proprietary rifling design comprised of six lands and grooves without sharp edges like traditional rifling. This design imparts bullet spin without leaving sharp impressions on the sabot jacket or foster-style lead slug.
Does that mean that you can actually shoot regular cheap slugs through it, even though is is rifled, without gunking up and fouling the inside of the barrel with lead?
Does anyone regularly shoot regular foster slugs through an ultragon rifled slug barrel without problems?