Yes, if I were to do a "9x57" I would cheat and use a .358" barrel for the sake of bullet availability.

I already have that advantage with my little Francotte DR, as it has .358" grooves. I'm loading the Hornady 250 grain round nose in it. I form my brass from .444 Marlin without a hitch. THere's plenty of chamber to accommodate the larger bullet and the necked-down brass without reaming or turning.

By the way, if anybody is intersted in a dandy small ring Mauser action, I have a friend with a couple of really good Mexican Mauser actions. He had intended custom projects but got side-tracked and now, I think, will sell them. If there is an interest, I'll inquire about the price. I think they would be pretty reasonable.

The Mexican Mauser can be made into a fine custom project.

Curl