Australia's ADI (Australian Defence Industries) makes a number of propellants designed to function well in temperature extremes. The powders are referred to as eg AR2006 etc. Some are called Hogdon in the USA.

But I forget which of the powders in particular were designed for use in hot climates.

If you look at their website there may be some information there.

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Personally I have never noticed any problems but none of my own loads are any where near maximum.