Rechambering Model 70 Safari Express in .458 Win Mag to .458 Lott

[Riflecrank]

Take a gander at how the exactly same powder charge in a .495 A-square beats a .500 Jeffery with exactly same barrel (26", 1:10" twist) and bullet weight, 570-gr:

.495 A-Square: 104 gr of H4895 >>> 2406 fps, sub-Pmax and most uniform of all for pressure SD/ES

.500 Jeffery: 104 gr of H4895 >>> 2348 fps, exceeds Pmax and wildly non-uniform for pressure SD/ES

 

[colorado]

That's just because you're running the 500 jeffery at the original 1920 pressure levels. With a strong action and new brass you can easily attain 2500 fps with a 570g bullet with the 500 Jeffery.