I have read and seen the "standard" 8mm listed as a 7.9x57. Possibly the 7.8 is the .318 bore version? Try posting in the Europe forum, may obtain some help there.
Yep, the "standard" 8mm Mauser is a .323 and is known as the 7.92 x 57, and is so marked on the barrel at the ring of some of the Mausers. The 7.8 is the older "1888 Commission rifle" chambering, and takes a .318 diameter bullet. Whatever you decide, DO NOT shoot regular 8mm Mauser stuff in that gun.
Wayne
