The importer may have electro-penciled the caliber marking under the front sight. Could be somewhat hidden by the cleaning rod (if you have one). If it's an original barrel, then it's 8x57 for sure. Anyway, American 8x57 ammo is quite mild (ie. Remington, Winchester). Not sure about the S&B stuff. Surplus varies from mild (Romanian) to wild (Turk), with Yugo in between.
I'd start with American stuff and work my way up. Read up on cleaning with water before you mess with surplus.
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