The M98 Mauser's design is quite strong enough to hold a magnum cartridge. If there is aproblem with Mausers, it isthat they were made all over the world by myriad factories, and the metal plus the heat-treatment of said metal varied wildly! Many are very strong, but some are not. The good thing aboutMausers is that even the "soft" ones are generally not brittle like some of the early Springfields were, so even if it fails, it will do so gradually rather than shatter! Just keep an eye on the headspace, having a good gunsmith check it once a year or so, for maybe three years. (Depending on how much you shoot it.) If it doesn't get larger in three years of shooting, it is probably OK.....

Unless you know exactly when & where it was made, I would NOT try to have it re-heat-treated. To do this properly, one must know what the material is, and how it was done originally.