Unless your Uncle rechambered his Argentine, it was probably a 7.65mm.
the 8x57 Mauser makes a fine hunting round, but works best when handloaded. For my Mannlicher rifle, I handload a 220 grain Sierra over 4064 powder. This is a great hog round. For Whitetails, I use 150 Speer Spitzer for 2900 fps and great accuracy. It is deadly on deer.
Nemo Me Impune Lacesset
"The trouble with our liberal friends is not that they're ignorant; it's just that they know so much that isn't so.".........Ronald Reagan