Good link, John.

"The Grasset catalogs mentions a MV of 1000 m/s (3280.83 fps) and ME 400 kgm (881.84 ft·lb) but the closest ballistic performance for the 6.5 x 61 Mauser published by DWM in 1930 is MV 945 m/s (3100.39 fps) and ME 351 kgm (773.82 ft·lb) with 3,5 g (54 grs) of R. 2 powder and 7.7 g (118.82 grs) bullet."

Might be the same as the 6.5x68's 12" twist.