They are 8x57. Yugo made mausers like the M48 are decent quality rifles. They are a little roughly finished compared to a nice K98, and the stocks can be very bland looking (elm stocked versions are sweet).
If you are looking at the Marstar mausers, I personally don't think they are worth $500+ with tax and shipping. I'd much rather get a Russian worked K98 for $300-$350.....much better deal IMHO.