The Wound Channel delves into a field test to see if you gain more velocity with ammunition that is warmer over ammo that is several degrees cooler.
With interest sparked in an anecdote from a Canadian sniper in Afghanistan who attributed cartridges warmed in the sun as producing higher velocities, TWC warmed some until they were hot to the touch and cooled others in an AC vent then broke out the chronograph.
The results are actually kinda interesting.
Source Article from http://www.guns.com/2015/09/04/does-sun-warmed-ammo-shoot-faster-than-cold-ammo-video/
