Yes this certainly seems a 8x58R Sauer chamber (IMHO of course; I can't locate my pertinent books right now).
As for the chamber cast, I just melt the nearest old candle and put the cast to fridge overnight. Works nicely for this purpose and I too find cerrosafe metal casting unneeded. And BTW I do use shooting glasses when melting and pouring wax.
With kind regards,
Jani