Re: temperature changes
7" at 500 yds. is way too much drop for just a temp change. That would be some serious velocity change. I could see if the ground was frozen hard, providing you were shooting prone with a bipod, and your shots being higher. I have seen where a Harris bi pod with the leg notch's set at the lowest setting having a bit of spring to the feet causing a low shot/group. If your barrel is not floated enough and making contact with the stock at 40 and not at a lower temp could cause a low shot, but prob not a low group. How about body position or even parallax issues? Somethings awry besides a huge swing in velocity.
AKA "BLACKTAIL SNIPER"
7mm-375Ruger smithed by Gunwerks
Stiller TAC 300
Broughton fluted 5.75, 5c @ 28"
Graphite Black Cerakote
GreyBull Precision Stock bedded with Devcon
180VLD's@3145fps. with 72.8grs. of H1000, 215m primer