We're going to need more information, and probably pictures to give you any info on this one; "Krupp" was the company in Essen, Germany that would've supplied the steel for building this gun, but I don't believe that Krupp themselves ever built any small arms (but were known for building cannon). The type of three-barreled gun you're describing is known as a "drilling", from the German word "drei" ("three"), and the standard pattern is two side by side shotgun barrels over a single rifle barrel. These were a relatively common hunting gun in Europe and Africa at one time, but I don't believe that they've ever been issued by the military except as survival equipment on German bombers during WW2. In short, we need more info, and preferably pictures, and the better and more detailed those pictures are, the more likely you are to get some good information. There should be a series of proof marks visible on the receiver and barrels when it is taken apart, and those will give an idea of when it was built. The manufacturer should also almost certainly be marked somewhere on the piece, likely either on the floorplate, the sides of the receiver, or the top of the barrels, on a rib.