The Ciener Ultimate Over/Under system is a modification of the Remington 870 shotgun by Johnathan Arthur Ciener. It is identical in purpose to the Knight's Armament Company Masterkey or the accessory weapon configuration of the Remington 870 MPS. The shotgun cannot be operated independently because of the yoke adaptor. The M16's magazine well must be used as a makeshift pistol grip. Independent stocks and grips for the 870 are available for use, but they are incompatible with the M16 barrel mount.