So I went back to your OP. Seems like there were groups to work with on your original test loads with maybe some seat depth variations that might yield better results. 40.5-41.0 of H4350 seems like it might work.
I use the Cortina method of seating depth testing. I start ~.020" off jam. I then have test groups 0.006" deeper than the last group. Total of maybe 5 or 6 groups. Somewhere in there, you should have two groups that look the best next to each other, meaning in sequence. I then load up a group 0.003" in between those two groups to split the difference. This usually gets me my seating depth which I find more important than powder charge.
If the above doesn't work, then a different powder/bullet test is in order. If that doesn't work then the barrel may be no bueano.
Have you tried any factory ammo?
You may try swapping scopes and see if your groups improve. I had a rifle I where no load I made would work in it, including factory loads. I was about to rebarrel and I decided one last test. I changed the scope and boom, sub moa with factory loads. I sent the scope back to vortex, they tested the crap out of it, and couldn't find anything wrong with it. So, it had to be some way I had the scope mounted despite me thinking everything was mounted properly.