Wait a minute....shotguns and slug guns ain't the same thing. You want to put a scope on a shotgun give some thought to a low power piece of simplicity like a Weaver K series (El Paso version) if your OK with artifacts. Or maybe a Leupold Compact of the same horsepower.
Slug Guns look like the pic below and use a different kind of scope. And they are muzzle loaders.
They were popular for target shooting a long time back.
And still are....