I used rifle scopes on slug shotguns for several decades before they started making scopes specifically for shotguns. My first scoped shotgun was a 20" barreledIthaca Deerslayer 12 GAsmoothbore with a Weaver J2.5 scope on it. This gun would put Remington brand Foster-type slugs into 4" @ 100 yards, which is about as good as is possible with a smooth bore.

You certainly CAN use a rifle scope on a shotgun! Just use a low-power model which will stand the recoil, AND has at least 4" of eye relief! Mount it as far forward as you can get it and still be able to see the full field of view...