Homer - the .458 2" allowed me to use any magnum brass I wanted. I did, however have to outside turn the 7mm Rem Mag and .300 Win Mag brass necks as they had too-thick neck walls.
.350 Rem. Mag., .338 Win. Mag. and .458 Win, Mag. brass was fine without turning.

The .450 Marlin needs .450 Marlin brass due to the wider belt they designed into the case. It is reported they did this so a .450 Marlin round could not be chambered into a .300 mag and fired, with probably disastrous results.

My chambers and my current reamer has a 3/8" throat. That throat allows the bullets to be seated out, which increases usable case capacity, indeed, it's as if the case was actually 2.375" long, not merely 2".

This is why I easily achieved the ballistics I did. I settled on these good shooting loads - 350gr. at 2,290fps, 400gr. at 2,150fps and 500's at 2,050fps.
Incidently, the same load was used with each bullet weight. Due to the recoil of the 500's, I stayed mostly with old style Barnes 400gr. spitzers at 2,150fps.
Today, I'd probably use 350gr. TSX's at about 2,250fps for everything from deer to griz.