Jim,
The marks on the side of the barrel show the duty load for your rifle use a 308.6 grain steel jacketed bullet. This is a heavy bullet for the 9x57R. A more common modern bullet would be the 250 gr. and I believe it is easier to find a satisfactory load with a bullet lighter than the one the rifle was regulated for, than one heavier. Of course, each rifle is a law unto itself.
BTW, it looks like the scope mount on the drilling is some type of lever release slide on quick detachable mount. If you remove it, you might discover a maker or marketer's name. Just a thought.
Mike