So your Druid Hill group still looks to be over 2” correct? The 85 grain game king is .106” shorter than the 87 vmax so that would open up quite a bit of case capacity. I have had the 87 vmax up into that realm of velocity but accuracy was shit. I too am getting the case splitting but I am still using the cases that I fired in the original barrel. Turns out more than just the necks were oversized. I couldn’t even come close to getting a piece of fired brass from the original barrel to fit the chamber of the new one. Even the main body was growing a ton. It took quite a bit of force in the resizing die. I am thinking of trying again with fresh brass that has never been fired in the original 6x45 barrel. Are you by chance using brass fired in the original barrel? My cases were only splitting with Tac and once with 8208xbr. Lever got me higher velocity and no cracked cases. I need to try cfe223 as well. That’s the only powder I have that I have not tried yet. I am only bumping shoulders back about .003-.004 using the Redding comp shell holders as well.
I think I will tape a heavy piece of steel flat bar to the handgaurd next time to take the weight aspect out of the equation.
You know, I did use this brass in the last barrel. That would explain that then.
I actually spent a good 30 minutes on the phone with the gent from Druid Hill (absolutely great guy to talk to!) & explained the ongoing issue to him. I actually called to see if he'd tell me what powder he used in the 85gr load & he was happy to do so. He was also happy to tell me that it's not commercially available either

When I mentioned that all this hoo-ha was with a Satern barrel, I thought he was going to come unglued! All his ammo testing & load workups are done with 18 & 20" Satern Liberty barrels & he tells me that they've been universally fantastic (although they're a much heavier profile) he offered to install one of his barrels to my action for AND figure out a load it likes for $250, which I thought was very decent of him. I'd take him up on the offer, but the standard Liberty barrels are much heavier & that sorta defeats the purpose.
As of now, I'm really not sure where to go. Obviously, I'm going to try virgin brass (like, brand new Starline or....... something) & see if that makes a difference. I'm DEFINITELY not buying any more freaking powder. If it won't shoot with X-Term, H335, TAC, CFE223 or the 8208XBR I'm picking up on Sunday, in some combination with Sierra 80gr SST Blitz, Nosler 80gr BTs, Speer 85gr BTs, Sierra 85gr HPGKs or 87gr V-Maxs, it ain't gonna shoot.
If, by next week I can't get 5 of some combo of that lot into 1½", both barrels are going back & I'm going to demand a refund. The other, heavier barrel I tried (Tactical Ordinance) can go back on & I'll see if that does any better this time around. It wasn't great, but it was, at least, consistent. Best group was nearer 1½", but the absolute worst was only about 3½ (unlike this......shotgun of a thing)