From your dimensions of the cases, it seems that they were blowm out to be used in a 458 Lott. And as Grumulkin said both are derivatives of the 375 H&H case. You can form the case down to 416 Rem, but you may need some Case Formming Dies to form the case down from .458 to .416.
[/quote]In necking down, annealing might help to prevent split necks from excessive brass working.
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+1