The powders that show less sensitivity to cold also are less sensitive to heat. It's different, though. I have tested a number of powders that didn't lose any velocity from 70 F. down to zero, but above 70 they ALL gain some velocity--which means that pressure also increases. The temp-resistant powders just don't gain as much.
I have seen some real wonky things happen with tradition ball powders on prairie dog towns in July. Those tend to be the most heat-sensitive powders of all, and I have actually seen a few rounds "cook off" when the shooter ran a cartridge into the chamber of a hot barrel and then paused to looked for a dg to shoot.
Haven't seen that happen with any of the newer temp-resistant powders.
