Don't have the cases to check but I thought the 6.5x68 has less capacity then the 264 WM but they are close. If I am correct it is between the 6.5 RM, 6.5x96AI and the 264 Win. Mag. The better powder for heavier bullets might be IMR8133 but most of the early 6.5x68s from Europe have a 1 in 11 twist so may max out with the longer 130 grain bullets. Newar ones have a 1-9.8 which is still a little on the slow side. 7977 might be optimal for bullets 120 grains or less.

The Nosler forum gives the 264 about two grains more usable capacity than the 68. There is some info there on an old thread about the 6.5x68.

I would just load with 264 data and stop two grains short of maximum or when the chronograph started showing a leveling off point in velocity. The RWS loads are hot so I would not try to exceed them.

Didn't the original Shuler version have the unusual chamber that allowed the shoulder to expand? Not sure about this one will try to look it up later.

If I only could get systematically outraged at all the component manufacturers and suppliers think of all the money I could save.

"When you disarm the people, you commence to offend them and show that you distrust them either through cowardice or lack of confidence, and both of these opinions generate hatred." Niccolo Machiavelli