I have an odd thought here, what is your outside temp? and what is the contour of your barrel? years ago, I took a trusted 270 to the range on a 95F day, and shot my normal three rounds at 15 minute intervals, and before the third shot the barrel was still HOT. The result was 1" between 1 and 2, and 2" to three. This is the only rifle I have this happen to, because of it's lightweight contour. But all my rifles open up at temperatures above 80. Also, the 300 is a hot load, it could be heating the barrel more. A thought would be to take as long as possible between shots on hot days, and see if the rifle is more consistent. Or if you can, save a target and fire the first shot on each range day at it, and see if the first shot hits in same spot each time. You have to use the same ammo each time however otherwise it's not a consistent test. Good luck man.