Wow ! You are in .416 WBY territory there.
Alliant Power Pro VARMINT is a great one:
3.275" COL with 500-grain TBSS in a 24" barrel, .458 WinMag:
77.1 grains >>> 2213 fps at no more than 60,000 psi
(published Federal Premium data)
That is with Power Pro Varmint?
Yes, here is the Federal load data edited to show how to convert the .458 Lott loads into .458 WM+ loads:
Here is Sir Jerry's "Tropical" load for his .458 WM+, throttled back a bit, sub-max load, sub-max COL, sub-max pressure.
He tried a couple grains more powder, no problems, and beat Federal's top load for .458 Lott with TBSS: