Have mentioned this before, not just here but in my chapter on powder/temperature in GUN GACK II, but temp-stability depends to a certain extent on the specific cartridge/bullet combo--and whether the temperature is colder or warmer. This is reduced considerably (especially in warmer temps) with powders designed and advertised to be temp-stable. But it still can vary some
TAC is very temp-stable with the right cartridge/bullet combinations, especially .223/5.56 and .308/7.62x51, the rounds for which it was designed. Outside those and similar applications it isn't so temp-stable.
Have found the same thing with ancient IMR4350. In some applications (such as 300-grain bullets in the .375 H&H) it has proven very temp-resistant in my tests. In other apps not so much
The Ramshot powder I've found the most temp-stable in my tests across a pretty wide variety of cartridge/bullet combinations is Big Game. Have also found it very accurate overall, which is why it's one of my favorite powders.
One thing I have NOT found, however, is that any powder advertised as designd to be temp-stable does not perform that way--at least at colder temps. ALL powders gain some velocity (and hence pressure) at much above 70 Fahrenheit. How much they gain often depends, again, on a particular application.
