Just to update my progress:
Again my barrel is the Faxon 6” 1/5.
This barrel is terrible. I have now put 14 different loads through it and it is dinner plate accurate at 40 yards. I don’t see evidence of keyhole, just garbage groups… or rather patterns…
I square every receiver before install, have assembled way over 100 uppers, 20 years experience hand-loading including wildcatting, etc etc, tried two muzzle devices, 3 different cans, and this barrel will simply NOT group. I contacted Faxon. I’m pissed.
Could simply be a sample of one, but wow. By far the worst barrel I have experienced.