8x57 RP and WW factory ammo is quite safe to shoot in your rifle.

It is loaded with a .321", 170gr. bullets at VERY low pressure just to be safe in these and M88 actioned rifles with .318" groove diameters.

If the ctg. easily chambers ammo loaded with .323" bullets, it will also be safe to shoot with those. Some .318" bores have too-tight necks for this and should not be fired with .323" bullets.

One easy method to see if this is the situation with this rifle, is to fire a RP or Ww factgory load, then try to push a .323" (8mm) bullet into the empty case.

If the .323" bullet will enter the neck of the fired case easily, you can shoot normal 8x57 ammo form Europe, IE: Norma which is actually loaded to the pressure that an 8x57 should be loaded to.

This test shows the chamber neck is large enough to allow the cae to expand and properly release the larger, .323"("S" type) bullet. If the larger bullet will not enter the fired case neck, under no circumstances shoot anything but WW or RP ammo, or handloads, loaded with .318" bullets.