Not a Mauser, but

[Amberg]

a rifle you do not find every other day on a period photo.

Please note the drum mags on the table.

[WaPrüf2]

Prima! Now you need to find one of the rifle on an aircraft...

[Loewe]

Very nice Wolfgang!

Did the picture have any information on the reverse?

[Amberg]

Sorry, nothing on the reverse. Since they have the drum mags, I'd guess 1917.

Over the years I've seen a few photos with the Mauser, but this is "my" first Mondragon. I remember one photo where the Mauser was mounted to the side of an aircraft.