Originally Posted by vino
I'm a little confused about what or why. . .
Are Remington bolt faces really that soft?.
It's unrelated to the hardness or softness of the steel in the bolt. If the primer pocket enlarges in diameter enough that a new primer fits loosely, the seal between the edges of the primer and the primer pocket can leak high temperature and pressure gas and flame onto the bolt face and cut/etch away the bolt face. This can happen even with loads that don't exceed maximum pressure ratings for the cartridge with loose primer pockets.
At higher (overloaded) pressures, it can happen with new brass on the first firing. Another issue that can increase the risk is excessive headspace, but I doubt that is your problem with the 300 Win Mag, since it headspaces off the belt rather than the shoulder, like the 25-06.
The cutting you have is better than the etching caused by a pierced primer, which can enlarge the firing pin hole in the bolt face.
I don't think you'll have any problems with continued use of your bolt, provided you don't keep leaking high pressure flame and gas around your primer pockets.
You're shooting loads at excessive pressures in my opinion, because you're experiencing this with more than one rifle. Repeated shots fired at high enough pressures will expand the primer pocket until the primers seat with very little resistance, and then gas can escape and cut into the bolt face. Check your powder scale against another powder scale, or get some calibration weights to ensure your powder charges are correct.