Re: temperature stable powders
To some extent, all powders very characteristics with temperature. Some more than others.
The temperature range you give is fairly extreme. Therefore, I would consider learning the temperature/performance characteristics of the powder each rifle likes best and develop drop charts for the highest and lowest anticipated temperatures. Or do as some, a summer and winter load for each rifle.
There ain't no free lunches.
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will be heralded as the man who kept elk from extinction.