<img src="graemlins/wave.gif" border="0" alt="[byebye]" /> RK,
"Cartridges of the World" lists the 7.92x33mm Kurz as a short cartridge for the German MKB42 Assault Rifle. They say "it is a short version of the 7.92 (8mm) Mauser cartridge".
Next, they do not show or mention a 7.92mm, but show a: "7.9x57mm J & JS (8mm German Mauser)".
The original Mausers (Gewehr 88)were chambered for the J cartridge and had bore diameters of .318" diameter. The later 1898 Model Mauser rifles were chambered for the JS cartridge and had bores of .323" diameter.
So I would assume the answer to your question is "yes", the 7.9x57, 7.92x57, & 8x57 are all the same cartridge, but may have a J or JS desigination, and can differ in bullet diameter.
COW advises slugging your bore, and do not fire .323 bullets in a .318 bore! <img src="graemlins/bigok.gif" border="0" alt="[thumbsup]" />