Rifled slugs through the smooth bore and saboted slugs through the rifled barrel. Try Hornady saboted slugs. I've had great luck with all things Hornady. I'm sure that others will have different opinions.
Did this with an 870 shooting Hornady SSTs at 225 yards with a Nikon Slughunter scope
Top and bottom are the first two shots when I was trying to figure out the holdover point, ones in the center are the last two. I'm confident the center would have been shot out if I had more slugs that day.