Targets are only 25 yards zeroing, just to compare what previous, good .458 WinMag loads would do for velocity in a larger case with same throat.
The .458 WinMag was loaded to COL of 3.395" in a 23" McGowen barrel and did a bit over 2500 fps with 80.0 grains of AA-2230,
with same 400-gr GSC HV:

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Graphic summary of the above, +/- is for standard deviation, not extreme spread:

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Results for 400-gr Speer with H4895:

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Ron aka "Rip" for Riflecrank Internationale Permanente
NRA Life Benefactor and Beneficiary
.458 Winchester Magnum, Magnanimous in Victory
THE WALKING DEAD does so remind me of Democrap voters. Donkeypox.