A chamber casting is always advisable on these guns. There is a good chance the 7.8/57 is for a .318 bore 8x57R Mauser. The 8.8/72 could be the 9.3x72R especially if it was proofed for lead bullets. These bbls often had quite deep grooves, thus a small bore size in relation to bullet Dia. Doesn't hurt to slug the bore either to determine groove dia for proper bullet dia selection.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra