Re: 7 x 57 ammo
I think that to make the best decision, you need to know if 1) these rounds have corrosive primers, and 2) if they are Berdan primed. Both of these things were common in WWII-era military ammunition.
A lot of people regard corrosive ammo as no big deal, if you know how to clean the gun properly. However, many people prefer not to mess with it. And as I understand it, not many people reload Berdan brass, so if that's what it is, you will have to use the original primers to get any use out of it at all.
I don't know enough about cartridge headstamps to tell you either of these things about your rounds, but someone here probably does. Good luck! (BTW, I think a Ruger single shot in 7mm Mauser would be an extremely nice rifle to hunt whitetails with.)