Two schools of thought, first is this a gun to be use for slugs and with another barrel for upland game or ducks. If so what range do you need to shot slugs to? If say 125 yards a cannalevered scope mount and rifled choke berenkie slugs works great. If over 125 say 175 or so fully rifled and sabots like winchesters partition loads.

And the other is a soley dedicated slug gun. Like a bolt, single shot, or pump with a fully rifledbarrel pinned to the receiver.