It's a Fukert that had a 9.2X72 initially and then sleeved to this 6.3X52R.
Cartridges of the World mention that 25-35 Win and the 6.5X52R share same external dimensions. They also mention that they have been loaded to aprox same velocity/energy on both sides of the Atlantic.
My gun is proofed for a 8 gm bullet.