Yes - they are .312, as noted in my post above.
I am also shooting them in my single shot 8.15x46R which has a .315" groove to groove measurement. 29 3/4" bl. length. It is indeed, a beautiful "old" rifle having a model 71-type Mauser action.
They are shooting quite well at about 1,750fps using 16.5gr. SR4759. I might try that one on a deer next season.