Basically, what 'gnoahhh' wrote is correct.

However, a big difference between the 1903 Springfield and the U.S. Krag-Jorgensen rifle is the rim of the .30-40 cartridge case.

A .30-06 cartridge case failure in the '03 Springfield may allow hot high-pressure gases to flow back into the Receiver and subject it to tremendous stresses.

Brittle single heat-treat 1903 receivers from all years (Springfield and Rock Island) are known to have failed. Multiple factors entered into the failures. A significant factor was 'out of specification content' of the steel alloy.

With the .30-40 cartridge, the rim serves as a gas seal. In the event of a split or separated case, the hot high-pressure gases are confined to the chamber and bore. There is less likelihood of gases flowing into the action.

FWIW - I am not trying to start or open the old tedious debate. People are free to make educated choices.

I do feel safe shooting .30-40 Krags.

I will not shoot low number Springfields. I do shoot a high number (nickel steel) 1903 Springfield and a Remington 1903-A3.