Raimey,
It's not easily visible in the pic, but the proof marks include the letters "U, F, W, S" all individually and all with crowns above them. Each barrel has the marking: "2,59 Sch.P" on top of "28,3 g Bl.". Also, on each of the two top barrels in a semi-circle back by the breech is marked: "KRUPP'S CHER - FLU SS STAHL" it's kind of hard to make out all of the letters, but I'm pretty sure that's what it says. Can you tell anything additional about the date of manufacture or anything else about the gun from that info? Thanks.
Austin