I strongly suspect that this rifle was rechambered in the US, after WW2, from 8.15X46R to 8mm-06. This would result in a lack of proof marks matching the dimensions.It would also result in a mismatch in dimensions because of going from rimmed to rimless case and widely varying dimensions of 8.15 barrels.This can all be dealt with by an experienced handloader, but it would have been much better if the rifle had not been rechambered in the first place.It was not, and is not my rifle, so I really have nothing to say about it.
Mike