I know I'm late to the discussion but a M70 Classic in 300 win mag becomes 458 3+1 with no real work right? Un-block the rear of the box, shorten the ejector-bolt-stop, and re-barrel that .300 WinMag to SAAMI .458 WinMag chamber, and VOILA ! You have a .458 WM+ capable of 3.6" COL. It's the use of a 375 H&H box that requires work but allows loading to a longer COAL thus beating the Lott? Yes. Or is the point to create lower operating pressures? Yes.
The .458 WM+ Unchained allows you to choose, either same velocity as the SAAMI .458 Lott but at lower pressure, or higher velocity than the SAAMI .458 Lott at same pressure as the SAAMI .458 Lott. Or just use the SAAMI .458 WinMag (3.34" and 60,000 psi) and get within 50 fps of the SAAMI .458 Lott (3.6" and 62,500 psi). Some perfectly safe loads for the .458 WM+ (loads at 3.6" COL or shorter) are unsafe in a SAAMI .458 Lott. Throat, throat ... Train, Train.
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.
