After WW1 The Kingdom of Serbs, Croats, and Slovenes/Yugoslavia had 180,000 Steyr-Mannlicher M.1895 rifles in 8x50mmR Mannlicher, both captured and given as war reparations. In 1924 The Yugoslavs chose the 8x57mmIS Mauser cartridge and the FN M1924 short rifle as their new service rifle, and to simplify logistics decided to convert all their preexisting rifles to 8x57IS, including the Steyr M.95 rifles. The contract was awarded to the Yakov Poshinger Arms and Ammunition factory in Uzice, Serbia in 1933, and work continued until the outbreak of WW2.
The rifles were stripped to the receiver, and the Mannlicher en-bloc magazine converted to a blind-end box loaded with Mauser-type 5rd clips. This involved adding a permanently-fixed metal clip in the magazine to retain the cartridges in the same manner as the en-bloc clip (NOTE: If this internal clip is missing, the magazine will not retain the cartridges when the bolt is open). The hole at the bottom of the magazine for clip ejection was permanently closed. Two guide notches for the stripper clip were cut into the receiver bridge.
The barrel was a typical Mauser-style stepped-profile, with the same sights and the same length as that of the FN M1924 rifle. The bolt face was modified for the smaller case head diameter of the 8x57 cartridge, and the extractor reshaped and enlarged to help secure the recessed rim of the 8x57 cartridge.
A new full-length handguard like that of the M1924 rifle was fitted. The stock used the same sling mounts and upper barrel band as the original M.95 rifle (the lower band was the same as the Yugo-production M24 rifle), and the M.95M mounted the same bayonet.
I wouldn't have any concern about shooting surplus 8x57IS in this rifle, or modern ammo marked "8mm Mauser" as long as the headspace checks out.
You remove the bolt by pulling the trigger forward.