Can rifled slugs be put in an over/under?

my dad and i are having a debate for when i get my shotgun i looked for slugs you can put in smoothbores which he didnt belive so i showed him but he dosent belive that you can put them in an over/under is he right or can they be loaded into one pesonally i dont see the difference between putting them in an over/under and a single barreled shotgun but if there is one let me know