or, maybe 9mm Kurz? I agree with another contributor, giving ein Scharfschuetzen soldat a cheap crappy double shotgun as a reward for sniping Allied personnel, just doesn't seem "Korrekt". If you go back to the first fotos, look at the milling marks on the side of the barrel lug- the foto with the gun broken open.

Easy to forge a script signature, such as Himmler's,even all of the Nazi thugs of that era. I would be very suspicious of this offering, and provenance would be very difficult. But still, there are TV shows about folks trying to find Hitler in SA, as the Mosad did with Adolph Eichmann in 1960--

"The field is the touchstone of the man"..