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.