My knowledge of big bores is limited. Please school me on what the .458 version (wildcat?) of the Remington Ultra Mag is cartridge called? What kind of velocity does it (realistically) put on a 500 grain bullet?

Isn't the .404 the basis for the 300/338/375 RUM series?

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"shoot 'em if you got 'em!"

In full length trim, it is the 460 G&A, in 2.5" length, the 450 G&A, balistics are roughly 2400 and 2300 fps respectively.

You should use the search function on this forumn and look up both rounds, as they have been rather thoroughly discussed.

You'll also find a debate about whether the round has a sufficient shoulder for headspacing or not.

My personal take is, the better options are either the 458 lott on the smaller side, and the 450 Dakota or 458 Rigby on the larger side.