hot loads....hot days

G'day. I'm looking for data on the effects of temperature on muzzle velocity.
I have had some loads go about 200f/s faster than what the load data says. Temp on the day, about 40c
I live in the tropics and the temperature often exceeds 40c. Australians hottest day on record ( 50.?c can't remember exactly ) is at the next town east, about 100km.
 
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