Hello rpeck,

Very nice rifles!!!!

About the markings, I know for sure 222,5 is the twist rate: 1 turn in 222,5 milimeters. Or, in the Imperial sistem: 1 turn in 8,7598 inches. Or, practically, 1 turn in 8,76 inches. The original for the 7x57.
I have two Mauser 7x57. In the older one, an original DWM sporter (1893 Mauser action), there is the same mark in the barrel under the chamber.

Good luck!

PatagonHunter