So it would appear that brass or freebore really aren't a big issue.
Wrong-O. Weatherby freebore
is a BIG issue, particularly when shooting Weatherby/Norma ammo, and when exploring the upper reaches of velocity. Always has been, always will be. Maybe 50-ish FPS is a decent place to stop when working toward Weatherby velocities, but rifles without Weatherby-style freebore definitely cannot handle the same powder charges as Weatherby rifles. Case in point: When I fired Weatherby 30-378 ammo in my Sako M995TRG/S magnum rifle so chambered, bad things happened. To its credit the rifle stayed together, but just about every other pressure sign you can think of (and some you wouldn't) showed up. It pained me to disassemble those Weeatherby rounds so they could be loaded for the rifle, but that is exactly what I did. The maximum charges I came up with were a full ten grains below advertised maximum charges in reputable manuals for Weatherby rifles.
