93mouse is quite right. The CROWN - crown/N proofmarks show it was smokeless proofed using the then "4000 atm Special proof powder". The standard M88 8x57I steel jacketed bullet weight was 14.6 gramm = 226 grains, service load. The proof date is 213 = February 1913. 125 is a typical Zella -Mehlis proofhouse ledger number, gun number 125 proofed that month. Suhl did not use such ledger numbers then. So the rifle was put together by the Zella-Mehlis guntrade, using an action scrounged from the government factories', likely Erfurt Arsenal, military production. This scrounging was not legal, but happened.
Though it is an 8x57I you may used the downloaded SAAMI specification American "8mm Mauser" 170gr loads. These are designed to be harmless in I-bore rifles. Contrary to popular belief the narrow bore is not very critical here. It is the chamber dimensions, especially a neck and throat area to tight to release a .323" bullet. So Remington at least load their 8mm Mauser cartridges with .321" bullets. If a .323" bullet freely slips in and out of a case fired in your rifle, you may even use European 8x57IS loads.