I wanted to know if you must leave a box of ammo in a car at what temperature is it still safe. In my state its about 90 degrees outside and the inside of a enclosed car can reach 110 within half hour?
Mandoguy, after modern ammunition is manufactured, it is ready to be stored for decades at desert temperatures. You don't have much to worry about up to 130-140 degrees. I've actually shot 20-year-old ammo that was stored in the Mojave Desert, and it was kicking at full power, so I know it will last at least that long.
The only heat level you have to worry about is at 275 degrees where the primers will start to blow up. Ammo is ruined by water, probably the only other thing you should worry about touching your ammo.