Mauser have a safety factor of close to 3 so they wont break. Even the pre 98' 2 lug mausers wont break, but they do have relatively poor gas venting and shielding so a blown case or primer may send gas and debris into your face. (ALWAYS WEAR EYE PROTECTION!) The mausers are so strong I shot a 96 Swede extensively, then had a bolt lug fall out when cycling it, broken off by an old fatigue crack. The one remaining lug held the bolt in place with no apparent problems. In retrospect I should have made up a proof load and seen what happened. I wouldn't be surprised if it passed proof with the one lug.
The typical "failure" mode in an overload for a mauser is to blow the barrel forward at least a couple threads. Bolt interior parts, the magazine bottom, and even the stock may get damaged by gas but the bolt body and receiver will stay locked and intact.
I'd guess the stories you heard of them cracking from heat treating are garbled retellings of the low number 03 Springfield heat treat problems - which only started happening when ammunition had quality control problems during WWI, or a few old cases of the very unwise reheat treatment of sporting Mauser conversions to harden them. Old time gunsmiths had a fetish about receiver hardness, but most mauser receivers were only heat treated enough to normalize them, and then are surface case hardened. This leaves the steel core soft enough to absorb an overload pressure by expanding instead of shattering. This safety feature is wrecked by heat treating, and I've heard of the side rails cracking when a heat treated receiver was dropped on the floor.
But after extensive use, or if poorly made, the surface hardening in the lug recesses may be lost and you may get lug setback from hot loads, the problem with a few Spanish mausers and probably the Chinese ones too. Otherwise, assuming normal care and use, a large ring mauser is the safest bolt action in the world.
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