Re: cold weather shooting
Couple little things we've noticed. Bring the rifles from a warm environment (house, pickup cab, etc...) into the cold, and you'll get mirage even on a grey overcast day. It's the just heat coming off the barrel as it aclimates to ambiant. We're going from 80 degrees to 10 degrees, and the it takes a bit for things to aclimate.
Have also noticed that as the ammo cold soaks, along with your rifle, it is good for a 1/4 to 1/2 MOA difference in come up at distance. We purposely chrono in the cold so that our numbers that go into the ballistic calc are close to the conditions that we shoot in.
Like others said, chrono your rifle/ammo combo, then cold soak it and chrono again. Note the difference and put it in your "tool box".