RE: Mossberg 12ga Sluggun
I just put a Mossberg rifled & ported cantilever slug barrel on one of my Mossy 500's. It came with a 3-9X40 scope on it, boresighted in the package from Mossberg. Shooting 2-3/4" Remingtom BuckHammers, it will tear up a paper plate at 75-100 yards. The scope is not my first pick for a slug gun but for 160 bucks, it will do. (I don't shoot it, it's for one of my nephews to use) I prefer a straight 4X scope (X 32mm) and have 4X's on two H&R Ultra Slug Hunters (one a 20 ga. & one a 12 ga.) but we are practiced to shoot over 100 yards. For alot of shooting under 60 yards like you said, I personally would go with a 2X scope.
Good luck with yours.