I wish I had a .458...

Back a few years ago one of the rags ran a piece about the whole series of Hornady "Magnum" cartridges. IIRC, the gist of it was that they use a special, proprietary mix of non-canister grade powder and some hocus-pocus loading techniques resulting in a form of compressed loads. Also IIRC, pressures were not deemed to be higher than SAAMI standards but may have been a bit higher than normal factory loads.

I do not know if they have a vibrating loading deck for the cases, or some form of drop-tubing of the powder or what. Higher QC could result in loads at SAAMI top levels I suppose whereas many factory loads are below max pressures and meant to be.