Concerning Springfield 1903 & 1903A3 Bolt. There's never been a " safety recall" so to speak concerning the Springfield Bolts themselves as far as I know! Maybe when they have "airbags" & no inference to members of this Forum including me!
Springfields as a wider mauser pattern genre, such locking surfaces on receivers are some few millimetres thick. The locking lugs abutting surface are considerably thicker and the inner striker hole is reflects a minimal compromise of that strength. Bolts for their surface locking area are considerably stronger than receivers, functionally a "shell". The termed "safety lug was intended as just that! Never to precisely abut in contact with the aft receiver bridge. Such would require an unnecessary dimension of precision. When the ultimate faliure of the bolt in shear, it was the "seatbelt". Krags functioned well with one locking lug altoether if in somewhat lesser pressure range. The point of a one "parachute" safety locking lug adequate where the forces dimenshed by predicate of bolt failure bleeding off most aft momentum. Such feature along with gas relief vents directing failure generated gasses away from the shooter face areas.
MGen Julia Hatcher, in his namesake "Notebook", found the "double heat treated" receiver the stronger of such and the later Nickel Steel receivers. Don't argue with me! Read the book. That said, the Nickel Steel became the preferred receiver material. I believe for the reason of manufacturing ease and greater tolerance to heat treating. The latter simply my take.
The 1917 Enfield, 1903 Springfields and many of the mauser 98 pattern variants have proven over decades to be entirely safe for normal pressures in an era when 50k would have been higher than normal but well within "the envelope". Where we get into trouble with handloads, etc.,, isn't so much in hot loads, but more often in overloads combined with such as bore obstructions, wrong diameter projectiles, extremely poor maintenance or incorrect parts/fitment issues arise. My belief most of the Twentieth Century mauser pattern rifles are sufficiently strong, of ultimate "worst case reasonably to be contemplated" is where the gun is has done its duty if rendered unusable as we can yet walk away. Add shooting glasses to that formula.
Of the original question, I remain without clear understanding per description. Perhaps Rockwell surface hardness test marks???
Just another wordy... as noted, my take!
Best!
John
