"...the unique craftsmanship..." I'll say. Really well done too. I'm guessing it was done for use out of a blind. Long eye relief scope with a very short butt stock would work well when sitting. Might have been for a wheel chair bound shooter/hunter.
There was a 6.5 x 57 Mauser. And a 6.3 X 53R R/K FINNISH. Be easier to convert/rebarrel one rimmed cartridge to another. Although there was a rimmed 6.5 x 57 too. Listed here under European Sporting Rifle. Warning: This site can keep you busy for hours. snicker.
Welcome to Cartridgecollector.net | Cartridgecollector.net