There once was this one albino Antelope buck...
that hung around with his harem in and about our Peacekeeper stage processing facilities. One evening on the swing shift, there were a few whitetail does hanging around, as well, and that little white buck mounted one of the whitetail does. Not sure which one was confused, but it indeed happened, and NO, I hadn't had my medicinal dose of group tightener that evening! I hadn't considered the possibility that such an event could actually produce offspring, but that ugly little critter you got penned up in the photo could've been his little one!!!
No help with the 45 degree cant of your string, but considering the beatin' yer ears most surely took while ridin' the rails on those 155's, maybe the brain housing group is canted!?
Only useful suggestion I actually have is to check that the bottom flat of the receiver is bearing full and not twisted in the wood, nor vise-versa. I'd have to believe that there's a high spot somewhere in the barrel channel that's pushing the barrel when it heats up, causing the stringing.....
What I've done to some sporter projects is to mark and file the top edge of the magazine box down so that I get about two playing cards' worth of clearance between it and the bottom of the receiver, and using a shim under the rear tang like Remington did on their rebuild program......Regards, Darreld.