 If the rifled barrels were the same caliber, then the three barrels were generally arranged in a triangle, both rifled barrels on top, or one rifled and the smoothbore barrel on top (this being known as a "cross-eyed drilling").If the rifled barrels differed in caliber, generally the layout would be an over/under using the shotgun and a centerfire rifle barrel, with a rimfire rifle barrel mounted between and to one side.These configuration, with shotgun/centerfire/rimfire barrels, are the most desirable configuration for modern collectors.