Changing the temperature of ONLY the ammo isn't the same thing as shooting the rifle and ammo when everything is at the same temperature. This is the major flaw in most so-called temperatures tests. For one thing, the temperature of the primer can change in a few seconds simply from contact with the bolt face.
The only valid way to test powders is actually shooting the rifle and load at varying temperatures.
Temperature-stability also depends on the cartridge/bullet combination. Judging powders on the results from one cartridge and rifle doesn't mean much.
