Nice report Chris, it's good to see all of the variations compared at the same time using the exact same ammo lot at the same temperature so no one can say it was due to conditions or other variables.
Did you find that 18 hogpack?
Have a few things you may want to try. 30gr H335 and those 130 Sierras loaded to 2.3"-2521fps from the 18" and a 5/8" group today.
I shot the revised 12" pistol with the 12 Twist and pistol length gas system today. I still need to adjust the loads but using the same 130s 8.5gr #9 hit 1040fps and cycled the action, 5.3gr "clays" hit 840fps and ejected the cases. by the time I get both up to 1150 they will cycle no problem.
I am going to try 7.2gr of clays next, it's a flake and fills the case better and it's faster so it should be quieter than the ss loads you were shooting when I was there.
I checked my notes when I got home from the hunt, using the TNTs 34gr of 335 gave me 3028fps and 30.5gr of RE7 hit 3066.
The Barnes should work well with H335 maybe around 31.5-32gr.
BTW- everyone that is worried about stabilization, the 130 sierra is the same length as the 110 Barnes and will both shoot from a 12" twist.
The 120 Barnes solid is as long as most 150's and will shoot 1/2" groups from the 11 twist I have.