If ammunition could detonate from the heat of being inside of a car on a hot Summer day then I would imagine that nobody would have "truck guns" due to the risk involved. Or at the very least, you would hear periodic tales online from folks who had ammo blow up in their car because they forgot to take it out.

In fact, I guarantee you that if there was any risk of such a thing ever happening, then ammo boxes would have warning labels against keeping ammo stored inside of a car.

That being said, be careful never to leave any cans of cola or rootbeer inside your car in the Summer, they will explode, leaving brown stains all over the upholstery which looks surprisingly similar to dried blood as it ages, which is bound to make any friends you might offer rides to extremely uncomfortable. I know this from experience.

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Shooting Comfort is bilateral.