Not a M70, but an older 700. It shot the old 130 gr. XC Barnes amazingly well. 2" 3 shot groups at 300 yards. The Barnes 150 gr. are a different ogive from all the rest. I originally was planning on shooting them in my AR-10, however because of their design, they wouldn't feed. I never did try them for accuracy in the 700.
I definitely second the bedding issue as the culprit for your issue. My theory is, even though the barrel has cooled, the stock/bedding is still heat soaked enough that it's causing the issue