I've run my side charging handle (modified) Armalite AR10 SASS to -14 F with no trouble. To compete at a shoot the rifles and ammo had to sit outside all night and a young man's M1 Garand actually froze up, although he did free it up. Its all in the type of lube you use. I use a moly bearing low temp grease with a sheen of air tool oil on it.
You know, I have been debating on whether or not to use the same moly based grease I use at work on my customer's vehicles for some of my guns, how well have you noticed it holding up? I honestly haven't really used it in a lot of applications where there's significantly dissimilar metals since in most automotive applications you're using it where steel is rubbing on steel, (i.e. a steel BCG sliding in an aluminum receiver) so I don't know if it gives the same benefits as it does on steel.
A lot of the good moly greases (aside from wheel bearing/general purpose greases you'd use for driveshafts/wheel bearings) tend to not be as tacky and using a thin coat goes a long way. Moly has the benefit of "filling in" the natural pores of metals and the sulfides create a nice natural slippery layer... I honestly have started using it as a general purpose lube for a lot of things simply because of those properties and less mess (within reason of course).
But the oil on your truck was fine? Hint...
I mean even lower quality 5w-30 is technically rated closer to -30°F so that doesn't entirely surprise me, it might crank a bit sluggishly; but should fire off.
Nobody has linked Garand Thumb's cold weather video?
I also am surprised by how long it took to link that video!
If it's cold enough to freeze in such short order, where is this water penetration coming from?
Condensation resulting from cold to warm/warm to cold is indeed an issue and affects smaller, tighter tolerance stuff first.
This was what a friend who operated in some frozen places mentioned, that it's not so much soaking the gun in water or freezing it in a block of ice; but just going from indoors to outdoors would cause enough condensation that the gun would freeze over. So they'd get in the habit of just leaving rifles outside so they don't experience drastic temperature changes.
I am sure tight tolerances play into this a bit, but in the case of the M14 I think part of the problem is that the stock it was mounted on had the cutout for the selector which allowed water to just soak the trigger mechanism and freeze it practically solid. It seemed a lot of the weapons failed because specific fire control mechanisms ran into issues (safety levers, trigger mechanics, magazine catches, etc.), I do wonder how many of the guns would have the same failures had they been stored vertically so that there wasn't as significant amount of ice build up in their more tight toleranced sections.
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To the OP I would say that most platforms will do fine in cold weather as long as you're being reasonable with handling the weapon. I wouldn't soak it in water or drop it in snow and let it sit for a few hours after firing off a few magazines. If you're going to go from hot to cold maybe set the weapon vertically and consider leaving the magazine out of the gun (I wonder if having the bolt open would help?) and give it a good bonk before using to bust off as much ice as possible.
Garand's video is extremely informative and interesting, bit it's much like Ian & Karl's Mud Test videos; they're very much pegged to the "extremely unlikely scenarios" side of the scale and are literally pushing the weapons to the their limits in situations they are not normally expected to be in often. I liken it to watching someone doing a video on "how long with each car brand run without oil?" Like it's absolutely interesting and does show the quality of engineering and where the weakest link is (i.e. an old Mercedes or BMW inline 6 is going to just chug along for a long time without any oil, while a modern Mercedes or BMW, or really any modern engine with variable valve timing, lifters, and/or advanced timing/valve control will probably seize up rather quickly). But it's really such a niche situation, like how often do you plan on not putting oil in your vehicle? So take those videos/comments about with a grain of salt, often there's a reason there are recommended procedures for handling/maintaining weapons in various climates to address these issues and mitigate problems; so it becomes a situation of "yes if you freeze the into a block of ice... it won't work well, so don't do that?"
