Not really a gun made for shot but you can have a new made double shotgun made will fully rifled barrels, rifle sights, designed and regulated for shooting slugs. I can think of several in both 20 and 12ga for less than $10k. Verney-Carron, Chapuis, and SIACE will make these. I am sure there are others but these were the first manufactures to come to mind.
I am looking for a gun that will shoot shot and solids. I am looking at a Tolley ubique gun right now. Does anyone here have any experience with this particular model?
