I don't believe I've figured anything out. Plenty of folks out there with higher levels of knowledge than I posses.
I have had at least one 264 win in my safe since 1995. I guess I was into this whole 6.5 thing before it was cool. With my newest Winchester M-70 extreme weather 264win nine twist I had significant issues with copper fouling in ~ the first 3" of the barrel that had to be addressed. It went straight from the box to the smith for bedding, a trigger, a muzzle brake, rings and an optic. Every 40-50 rounds it required a full decoppering as accuracy noticeably went south. A couple of more trips to a couple of different smiths for advise and re-checking, chamber casting, bore scoping to be sure there wasn't an issue. The only real credible suspicion was jacket skeiving. That just sucked to deal with. I started with Berger 140 hybrids and switched to 143ELDX and ended things with that rifle with Berger 130 AR hybrids. After 578 rounds and limited satisfaction I had had enough of that rifle and put it in the back of the safe and started looking for a solution. I never fire more than three rounds before allowing the barrel to fully cool to ambient with any of my rigs, regardless of chambering.
I recognized that with the 150g+ projectiles a nine twist is out of the question and an eight twist is marginal at best even at 264 win velocity with most of those projectiles looking for a 7.5 or a 7 twist. My project likely limits me to the 140g and heavier bullets with this rifle. Jacket stress, potential for skeiving and resultant bullet failure may indeed become an issue if I try to work with anything lighter other than solids.
The parts and reamer are at the smith currently and hopefully by the end of October I'll be able to start some preliminary load development. We will see what happens, I'll certainly share what I find.
