I'm not so sure about skyrocketing pressures in the .458 with 2,130fps loads IF the proper powder is used.
: I've been a wildcat ctg. shooter for many years, with one being a short .458 since the early 70's.
: That .458 2", 22" bl. loaded with either 4320 or H335, averaged 2,059fps. with 510gr. Winchester bullets or 2,062fps with the Hornady's. Those loads, while probably 'up there' were not excessive in my rifle, shot well, and in all my shooting with that rifle- probably 8,000 rounds and over 20 shots per case, has never expanded a primer pocket. I used .338 and .458 brass almost exclusively, only recently switching to .350RemMag.
: The chamber was long throated and actually equivalent to a length of 2.3" if measured against cannelure height of seated rounds.
; The ultimate test for high presure, is brass life- many were discrded due to split necks, but never a primer pocket. I still have some of the original brass, still going after over 30 years.
: With it's greater capacity & with the proper powder, there should be no problem getting factory-spec velocties from the .458 Mag's 2.5" case.
: I firmly believe there were problems getting that velocity with some of the powders people tried to use - mainly a fault in choice of powder, not in the round itself. Will it do it with large sticks of powder- probably not - but with proper ball or short stick powders - easily.