Very rare, pre-WW2 ammo designed by Leonid Kurchevsky for his hunting rifle.
More details can be found here: http://www.6ppc.ru/index.php?option=com_content&task=view&id=257&Itemid=43
Thanks for sharing!
Very interesting box!
How is this cartridge related to the well known “other” 5.6x39R and the 6.5x39R?
Here the 5.5mm:
And here the 6.5mm (all images from the web):