I can't pull up your photos to see the caliber marking--is it 7x57--or 7x57R, which would be more common. A rimless ctg. is not impossible, but less likely. Large difference in the ammo cost and availability between the two rifle rounds over here(although I suspect most Merkel users don't exactly burn up cases of rifle rounds).

About as practical a pairing of "old school" chamberings as you could wish for!