This is one of my Santa Barbara actions. Currently has a pressure test barrel with a strain gauge mounted.
Stuck it in the Wilson Rockwell tester, came out with 26 Rockwell on the C scale. Certainly OK for most standard cartridges. I would not use it for the big cartridges as you remove too much metal from the bottom lug area. And making a lapua feed out of a Mauser would be a real nightmare.
I have seen lower hardness values for these actions. And for other Mausers, as low as 12 on the Rockwell C scale.
My advice? Have your actions tested before re barreling to a modern cartridge. One trouble with the big cases is a lot of guys tend to "tip the powder can" in search of high velocities and run the pressures up.
The pressure test barrel in action:
And the best way to go for a 338 Lapua: The CZ550 action. This one has a No.6 Pac Nor at 30 inches long.
Cartridges are a 308 and the 338 Lapua.