I feel your pain. I have definitely been there. I just wanted to share my experience as it may give you a few different ideas.
So I had a pac-nor stainless steel super match grade barrel installed on a winchester action. I did all the usual reloading variations from different powders to different bullets/seating depths to get it to shoot (just like you are doing). I just could not get the gun to shoot better than 1.5 moa. So I sent the barreled action back to pac-nor, and their response was "why didn't you send us this gun ealier?". They checked it out and determined that they had in fact drilled the counterbore of the chamber incorrectly. Honestly, I did not fully understand the specifics of how/where the problem was in the chamber, but they fixed the problem that they were able to see. They also said that with this kind of issue, that they really had no evidence one way or another that it would in fact cause an accuracy problem... Overall I was very happy with their customer service.
Took the gun to the range... still would not shoot. So after a lot of painful hours and dollars spent shooting and lots of experimenting (details are not important) I sent the scope back to Leupold. They immediately found a problem in the windage/elevation control mechanisms, fixed the problem. They had the same exact reponse as pac-nor: "please do not hesitate to send back the scope in the future if you have any problems, and don't wait so long next time!".
Straight to the range and the rifle was shooting 1/2 - 3/4 moa. So the problem really was in the scope all along... I technically have no way of proving this, but I don't think pac-nor's chamber issue was the cause of the problem. Leupold verified the problem and fixed it and then the gun shot great. and I'm talking GREAT. and now the gun will shoot just about any load and any powder well, and when you dial it in it's simply superb.
So my personal experience is that when you have a gun that is a shooter, it simply shoots just about anything pretty well, and then a tuned load is amazing. And from the description of your gun, you've got everything in place... that gun should shoot
! And when I read your post it reminded me of my 338 win mag and maybe you have some component with a small flaw/error in it ??
When you add up the cost of gunpowder and bullets, and time reloading and shooting, you quickly see that paying for postage back to pac-nor or your scope back to the manufactuer to have them check it out may very well be worth it. There was a point when I was cursing pac-nor and sweared I would never get another pac-nor barrel (and leupold!). But now looking back on the experience (it was many years ago) I have had a few more pac-nor barrels installed on different guns and they ALL shoot very very well. So I really don't know any specifics about your gun, and maybe none of this info will help you at all... It just struck me that you've got a gun that should really shoot well, and it looks like you are doing every trick in the book to make great ammo for it... just don't give up on it!
Good luck and let us know if you figure it out!