One thing that makes me nervous sometimes is leaving a loaded gun locked in my car in the summer heat here. We hit the mid to upper 90s on the hottest days, and that's got to be multiplied inside a sealed car. Are there any dangers from the heat getting to the bullets?

Also as hot as our summers are, our winters can go the other extreme in cold. Let's say I go out to my car at 9pm in 15-degree weather and am met by a dopehead wanting me to go back in and get him some free Oxycontin. If I were to shoot him, could the heat from the bullet tear apart the very cold gun?

Nothing to worry about unless you're lugging around old waxed paper shotshells...

Smokeless powder does not love long term elevated temperatures, but essentially all that does is deteriorate the powder faster (less velocity). If you are REALLY worried about it, change the ammo annually by shooting up what was stored in your vehicle and replacing with either new ammo or ammo that has ben stored in more moderate temperatures.

There are some conditions that can cause pressures to shoot way up; the classic" scenario is a hot reload for a large caliber rifle is developed in cool weather in the states, then taken to a tropical country for hunting. A load that was to-the-wall max in an already high pressure cartridge can go "over the line" for safe pressures in tropical heat. <shrug> That's not your case; don't worry about it. (and it's not as common a problem as some think, anyway)

Cold weather? Don't worry about it. It will fire fine with no harm to the weapon. However, there are things to remember about bringing a cold piece of metal into a warm house - moisture will condense on it like on a cold beverage glass in July. Best to keep it in a sealed moisture-proof bag (ziplock) until it is at room temperature if you bring it in from the cold. The other consideration for extreme cold is that some lubricants will become so stiff - even just a light film - that the weapon may not cycle properly, making it a single shot. Again, that's not a common problem in temperate climates, but if you regularly get arctic winter temps, it may be. There are two solutions: No lube (fairly simple solution) or fancy lubes designed for those extreme low temps.

Thanks, that puts my mind at ease. And I appreciate the tip on avoiding a 'sweaty gun' when you bring it inside in the winter! <img src="/images/graemlins/laugh.gif" alt="" />

I'll second that. For a defensive weapon, meaning you bet your life on it, you should go through enough of your defensive rounds that the ammo never gets old.

I'm no AR expert, but I believe the twist was modified from the original design at least in part for cold-weather accuracy. Someone more knowlegable can expand or correct, but that's not really relevant to a personal defense weapon.

FWIW, the temperature inside a vehicle can usually get about 30F above ambient.

Unless you are storing it in an oven, don't worry. I know a lot of firefighters, and they aren't worried overly about it when they go into a burning building.

As for super cold... Maybe at 40 below, but I just don't go outside at that point. And that would be some very finicky gas operated stuff. Anything made for the defensive market should be fine.

And even if you vapor bag, you want to clean if you bring it in. There will be some moisture.

Oh, and the rifling change on the M-16 from A1 to A2 had to do with the switch from a 55gr bullet of medium hard lead to a 62 grain one with a slightly softer lead with a harder penetrator tip.

I wouldn't worry too much about heat and cold on standard ammunition loads. Two other things that temp extremes effect is your zero can move and lubricants change properties. Check your zero and use the lube sparingly.

Gun metal can get brittle down at liquid nitrogen temp levels. Unless you are travelling to the dark side of the moon, I wouldn't worry too much about shattering a cold gun by shooting it.