Yes, I know the alloy. It's a very common one that hardens and tempers easily. Since the only part of a Mauser receiver that needs to be even partially hardened is the rear of the receiver ring where the bolt lugs engage, it's not particularly difficult to do. Even if those lugs aren't perfect, how many thousands of rounds being fired would it take to make a measurable difference in headspace? Annealing and re-hardening an 03 receiver that's harder than woodpecker lips all over is a different kettle of fish entirely, and is something that I won't attempt.
