'Man-Goat' - IIRC - Early 8X57mm Mauser ammo used a .318" diameter bullet. This was used in Model 1888 Commission Rifles and, as 'reincarnated' stated, in pre-1904 German model 1898 Mausers.

In the early 1900s, the 8X57mm cartridge underwent improvement, most notably, a change to a .323" diameter Spitzer bullet. The bore size of German 8mm rifles intended for this cartridge was increased to .323".

Some of the earlier German rifles were re-bored to .323" and the barrels were marked with a stylized "S". Some weapons, especially Sporting Arms, were not so altered, hence, the need for caution (and slugging 8mm bores).

Your Egyptian FN49 was made for ammo with a .323" diameter bullet. However, your rifle is gas operated (like the M1 Garand).

Like the M1, I am sure there is a range of bullet weights (and profiles) and specific propellants that give the proper gas-port pressures for correct and safe functioning of your FN49's gas system.

(It would probably be good to ask about proper 8X57mm loads, for the FN49, on one of the Military Surplus weapon forums).