Another possibility, one I was surprised the more adverturous didn't persure, is my rendition of the .458 Alaskan. This is none other than the .450 Alaskan (.348 blown out and necked) with the rim turned off to .532"(magnum bolt face), extractor groove cut and chambered in a Mauser, Rem or WW M70 as I did. The case capacity is roughly 4 gr. greater than the WW.458 mag. and 2,200fps is easily achieved with 500gr. bullets.

It only takes about 15 seconds to alter a case. Left with the rim intact, it's a rimmed case for a single shot, same extractor/ejector as a .45/70. Turned into a slight rebated rim as in the photo, it uses a magnum extractor/ejector.