For a shotgun scope, there are two important factors. One is eye relief, so you can get your eye far enough AWAY from the ocular lens to not get hit when it recoils!! The other is its ability to withstand recoil effects!! Slug guns have a heavy recoil, compared to most rifles!! A scope which can last indefinitely on a .30/06 might not endure one season on a slug shotgun!!

Keep yore powder dry!!