All brass fails eventually. That being said a high pressure round like the 300 Win Mag you expect fewer firings of full pressure loads than something mild like a 30-30.
If you want long brass life, you can load 30-30 pressure levels in the 300 Win Mag, and neck size.
Or you can cram a bunch of magnum rifle powder in it topped off by heavy bullets and "reach out and touch something."
Personally I find that auto-loaders are much harder on brass than any bolt gun.
Machine guns are awesome until you have to carry one.