The first version of the German 8mm Mauser 
cartridge was introduced for use in the Model 
1888 Commission rifle and was officially dubbed 
the 8x57mmJ.  A 1903 variant was called the 
8x57mmJS and the two were NOT interchangeable, 
but appear to be.  The development of the two 
types of the "same" ammunition has cause much 
confusion about the 8mm Mauser, particluarly in 
the U.S.

    The primary problem is that the two 
cartridges use different size bullets!  The 
earlier cartridge uses bullets of .318-inch 
diameter, while the later employs .323-inch 
diameter bullets, a full five-thousanths of an 
inch larger!

    Use of the smaller bullets in a barrel made 
for the larger results in poor accuracy.  
Reversing the mismatch, that is, using larger 
bullets in the smaller bore can result in 
excessive chamber pressures and possible damage 
to firearm and/or shooter.

    American ammunition makers have dealt with 
this issue by intentionally UNDER-loaded their 
8mm ammo.  European makers cut no such corners, 
and provide both types of ammo in full-power 
flavors.  It does not seem to be a problem for 
the Europeans.  Before shooting an unfamiliar 
8mm, it is a good idea to have the firearm 
checked by a gunsmith as to type.