.458 Winchester Mag.

SAAMI - max - 60,000psi CIP max - 62,000PSI
SAAMI - max - 53,000cup CIP max - 54,000cup

As to .458 - Hodgdon 2014 Annual Manual listed as 24".

300gr. 2,730fps @ 48,100cup
-------2,753fps @ 50,500cup
-------2,793fps @ 51,300cup

350gr. 2,496fps @ 38,700cup.
-------2,548fps @ 51,600cup.
-------2,563fps @ 49,800cup
-------2,589fps @ 49,400cup

400gr. 2,362fps @ 44,300cup
-------2,407fps @ 51,100cup
-------2,349fps @ 42,500cup

450gr. 2,235fps @ 48,300cup
-------2,220fps @ 48,200cup
-------2,220fps @ 51,000cup
-------2,005fps @ 43,000cup

500gr. 2,152fps @ 48,100cup
-------2,163fps @ 50,300cup
-------2,140fps @ 49,700cup
-------2,123fps @ 50,300cup

Incidentally, the 2014 Annual Manual has an article on the .500 Nitro Ex., by Bryce Towsley.