Regarding my plan to have a Mauser M03 rifle with a couple of barrels in 6.5x65 and 8x68S, they suggested a 8.5x63 instead of both.

"Take a single 8,5x63 barrel instead. The 8,5x63 covers and exceeds both the 6,5x68 and the 8x68 S factory loads by bullet weight, velocity and so efficiency:

8,5x63 @ max. p (~62k psi) is good for:
105 gr 3840 fps
140 gr 3380 fps
180 gr 3020 fps
225 gr 2750 fps
250 gr 2650 fps
275 gr 2500 fps
300 gr 2400 fps"

Basically a .338 on the 9.3x62 case with the shoulder further forward than a .338/06.

What do you think?