Hard as it was for me to believe,
I was told recently by someone I TRUST that it's mostly about "Barrel Time" which gets to the air density inside the barrel. This determines how long it takes the bullet to push the ambient barrel air out, thus potentially causing variations in frequencies of vibration.
I must admit, is difficult for me to "drink that Coolaid" but I am going to do it. Temperature sort of dictates the air density but not totally. It would be my guess, based on the simple air density theory, that trying to corelate a number of varying temperatures in a mixed heat invironment would be madening and not productive. Monitoring air density may also prove to be the same.
This "Barrel Time' thing was also discussed with me last March at a long distance range I visited. A man I was talking to there was in the process of developing a long distance Wildcat round. He also said finding the tune was mostly about barrel time. He had a computer program and a hand typed list provided by a ballistition to guide him. It seemed like some sort of Black Magic to me at the time but I didn't discount it out of hand.