Very interesting Sir Ron, to be a fly on the wall of your machine/load shop, LOL!
Shell belt loops loaded tight for ease of extraction, final zeros checked, 458 WM+, 404 Hammer/500gr TBSS at 2500-2300+ fps respectively, old Holland double 500-450 3-1/4" Nitro Express ready with 480gr Hornady DGS/DGX's at 2148 fps over 105gr H-4831, it's a 75gr Cordite rifle, i'm much lower than that with the H-4831 pressures, plus, they'll stay put in all temp extremes.
