I'd bet that the forgings and barrels came from Ferlach. I'd also suggest, but not bet, that they might have been a gun in the white when they crossed. The prototype theory seems plausable, too. This could have been an experiment or a masterpiece (one of the sons turning master) that went right and was judged worth of the serious decoration. Note that the engraving in 1955 would not have been that big a deal as engravers then were not considered, or paid, as the artisans they now are.