Minimal temperature for an AR-15 rifle?

So there's a guy I meet on Facebook(I know it's on the internet but whatever), he claims that USA will rule the entire planet, and I told him that that would be impossible, mostly because nations such as the Nordic Nations, Russia, and Canada is very far North the climate here is very cold would be a suicide mission(example Wehrmacht's invasion on Moscow), but over to my questions.

1. What is the minimal temperature an AR-15 Rifle(M16A4, M4, M4A1, SR-25, M110) can operate in before malfunctioning?

2. What is the standard life-time for an none-cold climate designed fire-arm in ~25 minus celsius?

3. How much experience does the US Armed Forces have in Artic Warfare?

4. At what temperature does cartridges "freeze" and stop work properly (common problem for Wehrmacht when they made an attempt to invade Moscow)?

5. What is your opinion about this guys nonsense that he claimed?

•Rubbish.

•Bullshit.

•Possible.

•Maybe.

•They have a good chance.

•Own opinion.

//Cheers