When you heat treat metal, you do it twice. First heat it, quench it. Its quite hard and brittle. Now to make the metal usable, you re-heat it and draw the heat out slowly, its called tempering. Just how much tempering depends on the use of the steel or how hard you want it.
Or you can add nickle to the metal to make it elastic.
We know that when an explosion occurs in the chamber of a rifle, something has to give so the metal in the action and barrel has to be elastic enough to allow it to expand and contract.
Kind of like hitting a piece of glass and a piece of lead with a hammer (extreme but you get the ideal) the glass being hard and brittle shatters, the lead being soft gets smashed but doesn't shatter.
Its the same way to an extent with rifle actions. You heat them, quench them they are brittle, they can, and have shattered. If you draw the temper out of the receiver (second heat treatment) the metal is allowed to give much like the lead mentioned above.
Consult Gen Hatcher's Hatcher's Notebook, and Capt Edward Crossman's Book of the Springfield, to read more on the subject. Both have reports of destroyed receivers do to the single heat treatment.
Now we know there is a difference in the pressures of different rounds. The 30 cal or 30-06 military round is loaded to moderate pressures, (consult reloading manuals regarding the difference in loading for M1/M14, etc, compared to the loadings for the modern bolt action rifles).
You MAY get by by shooting low pressure rounds, but you run the danger of destroying the rifle and personal injury. This hazard is increased by using modern ammo designed for modern bolt guns.
The CMP probably has the best Surplus Rifle Armors in the country since that is all they deal with. They conclude that the early Springfield's and Rock Island rifles are not safe to shoot.
The CMP has no way to determine what ammo the competitors use. They are commissioned by Congress to conduct matches and clinics and to do that safely, hence the rule for Low Number Springfield's.
One can do what he/she wants with his or her rifle, but I am a CMP GSM Master Instructor, allowing me to conduct Sanctioned Matches and Clinics, am required to do so following the CMP GSM Rules.
I also agree with the rules, but that's my personal opinion. What I do on my own, (and I do do some dumb stuff) is one thing, but ethics require I follow the CMP rules to the best of my ability.
CPT USAR Ret
USAMU Sniper School Oct '78
Distinguished Rifle Badge 1071