James Rummel has a cool (ha!) post about temperatures and ammunition.
What with summer pretty much here in Texas and the car interior getting mighty hot, this information could be relevant to some.
In short, it seems like dangers of “cooking off” are unfounded, but it will degrade the ammunition and could actually risk problems if fired when too hot because of pressure increases.
Stuff From Hsoi 
My favorite powder, WST, is inversely temperature sensitive. The hotter it gets the less power the load makes.
I would love to see some real world tests/data of common carry ammo.
Of course, we can’t know what ammo manufacturers use in their ammo so…. we just have to tread carefully.
But yes, it would be interesting to see some real tests. It sounded like the CorBon people were going to do some… would be cool to see if they actually do.