Would a gun work in space?

In today’s question about firearms needing oxygen to work in space, Bricker’s answer is spot on so far as chemistry is concerned but I would be more concerned about lubrication. Even if the lube is not affected by vacuum (boiling off, for example), when it is cold* it is liable to get thick enough to gum up the works. If you try using the weapon dry with no lubricant at all, cold welding is a worry.

I read a thriller story some years ago set in balls-off-a-brass-monkey Arctica. The protagonist needed to enter a dwelling with a potential antagonist inside. He left his rifle outside but took a pistol in with him, knowing he was rendering the gun useless when it was taken back out. The warm, moist air would make dew condense on the piece, okay while inside, but it would instantly freeze outside rendering the parts immobile until he could disassemble it and scrape it all off.

*Yes, it is not cold all the time in space, but it can be.

Because there is no air or water to disperse and modify heat, the heat also would probably damage a weapon by expanding the metal parts. The daytime temperature on the moon is that of boiling water.

For people who like the sort of “what if” questions in this column, Netflix currently has a show called Hollywood Weapons: Fact or Fiction? Each episode takes a scene from a movie, and tests it under more or less realistic conditions, to see how realistic the scene is. For instance, the first episode tests how effective pistols are when fired underwater.

That sounds like it’s definitely worth checking, especially in the light of the fact that some of the stuff they portray is just plain ridiculous.

If you watch the chase scenes, for example, in the movies “Collide” and “The Hitman’s Bodyguard”, it shows cars being shot to pieces while, miraculously, the occupants inside remain basically unharmed. Sometimes, you even see sparks off the cars that imply that the body of the car can somehow deflect bullets when, in reality, even a 9mm slug will pass through the skin of a car like it was aluminum foil.

In contrast, every time there is a drive-by here in Chicago where bullets are fired into a car, the occupants are always hit. If lucky, they are just wounded but, most often, they are killed outright. That happens in just a relatively brief time, not in a long, ongoing chase where dozens of bullets are fired at a vehicle.

Interesting - so when Neil Armstrong was standing on the Moon in that photo with sunlight on him, he was at 200+ F degrees?

Well yeah, but in space no one can hear you scream.

This was a plot point in one of the episodes of Firefly - they “solved” the issue by having the rifle inside a separate spacesuit. I always wondered whether that would work.

He would have been without his space suit.

Ah yes, Vera. Reminds me of one of my favorite lines in the series, from when Jayne offers to trade Vera for Saffron:

“My days of not taking you seriously are certainly coming to a middle.”
-Mal

It would work for one shot, but wouldn’t the released bullet breach the suit on its way to its target, thus letting out all of the air?

Yes. I can’t remember if he shot once or a few times in rapid succession but the general principle seems sound. Aiming would be a bitch but this is fiction anyway.

The experience with WWII machine guns at high altitude/low temperature was generally not to use any lubricating oil. At least for US .50 Brownings that was found to be the way to go, with no problem from lack of lubrication. Although that wasn’t space cold. And in general you’ve pointed out a real issue. Some autoloading guns in history did not work reliably at low terrestrial temperatures, at least when applying common practices (like lubrication with particular oils) where they did work at normal temperatures. In the much lower (or much higher/lower, if you don’t shield the gun from radiant solar heat) temperatures of space you’d really want to test it I think rather than just declaring it would work.

This question is generally asked/answered in terms of whether modern guns’ primers and propellant rely on the atmosphere. Which of course they do not (though that’s not true of every gun ever, a matchlock wouldn’t work in space). But that’s not quite all there is to it.

Besides the temperature issue, there could be issues with gravity. Well designed repeating/autoloading gun mechanisms don’t rely on gravity to help feed the next cartridge, and ideally are insensitive even to +/- a few g’s (on a/c). But not all such guns used in history were well designed. Then if a shooter is floating free in space that would potentially at least slight effect the operation of a recoil operated autoloading mechanism which is powered by relative movement of bolt/barrel v the rest of the gun. It could be enough of a difference between bolt/barrel weighs ~29# (say an M2 HB machine gun), rest of gun and shooter weigh ~infinite because rigidly attached to earth, and rest of gun/shooter weigh say 200# (free floating #150 shooter) to at least slow down the cyclic rate. A smaller effect on blowback or gas operated weapons is that the gas pressure in the barrel would drop slightly faster with a vacuum at the end of the barrel rather than earth’s atmosphere. That would be tiny I guess though compared to the small effect on recoil operation.

Temperature (relative thermal contraction among parts) though is the thing I think most likely to mess up the general statement ‘of course guns would work in space’.

Of course, even if they didn’t need to put the gun into a spacesuit, I don’t mind that episode, because all it really means is that Jayne (and maybe Mal) thought that they needed to. Which is perfectly reasonable, because Jayne is a total idiot, and while Mal has some smarts, they’re mostly not geared towards science.

And the first bullet would of course breach the suit, but that’s also fine, because the biggest issue with temperature in space isn’t the hot or the cold. It’s the insulation. An object that’s at some temperature will take a long time to reach any other temperature (whatever that temperature is), unless it’s generating its own heat internally. And if it is generating heat internally, even if it’s shadowed from any nearby stars and so the effective temperature of its surroundings is very low, it’s likely to overheat, because it can’t dump that internally-generated heat quickly enough.

Cold welding is a bit of an overplayed concept. Yes, it is possible, but the surfaces have to be exceptionally clean and flat. Unless you’ve gone out of your way to clean the surfaces to a high degree, you won’t experience cold welding. The crud that naturally settles on everything outside of a cleanroom is enough to disrupt it.

Galling is a related but distinct phenomenon, and was the infamous source of the Galileo probe’s failure to unfurl its high-gain antenna. It is also likely to happen only on clean surfaces (though not to the same degree), and only with high contact pressure. It could be a problem for a gun but even a tiny amount of lubricant (dry or not) is likely to prevent it.

That’s not really that hot compared to guns being fired rapidly. I’ve seen plenty of rain drops hiss into steam on hot barrels. I even know someone that got a pointed reminder that he should have changed barrels on his machinegun much earlier. The point of impact suddenly started to drop in the middle of a long burst as the steel of the barrel softened and deformed.

Starting hot with no air for cooling makes heat a bigger deal for repeated function. I have a hard time seeing any reasonable design not firing at that temp, though.

The Soviets actually deployed and test-fired a 23-mm cannon in space. (Three of the Soviet Salyut space stations were actually part of the Almaz military space station program; “Salyut 3”/Almaz 2 carried out the test firing–after the crew had already left, in case of any problems.)

Radiative cooling gets pretty efficient at high temperatures.

Consider a gun shooting 5.56 NATO rounds at 900 rpm, or 15 rps. They have a muzzle energy of 1600 J. I don’t know the thermal efficiency of a typical round, but let’s suppose it’s 33% (sorta typical low for a heat engine). That means 3200 J per round or 48 kW of heat to get rid of.

The Stefan–Boltzmann law says that radiation (for a blackbody) is 5.67e-8 W/(m[sup]2[/sup]K[sup]4[/sup]). That is, it’s proportional to the 4th power of temperature.

Let’s also assume we have a 1 m barrel and a 10 cm diameter (mostly cooling fins). That’s a surface area of 0.3 m[sup]2[/sup].

Plugging in, we get 48000 = 0.3 * 5.67e-8 * t[sup]4[/sup]. t=1296 K, or 1023 C.

That’s warm–orange-hot, in fact–but not crazy out of bounds for known materials. Dealing with thermal expansion and ammo self-ignition might be a problem, but it should be possible for the gun to survive in steady-state.

Thanks for the back of the envelop calculations. I hadn’t considered that.

I found this paper for cookoff temps of propellant in cartridge cases loaded into hot chambers. 151.4-153-4 C seems to do the trick so that’s an issue even with designed for space extra large radiative fins.

If the chamber is made from some low thermal conductivity material–a ceramic or the like–and the round is cycled quickly, then it seems like you could avoid cookoff. The round has some thermal mass and won’t heat up instantly. You’ll need other (low-temperature) radiators to keep the mechanical parts cool, but if you can keep a thermal barrier between the hot barrel and the rest, it seems vaguely doable.

And a few more variables:

The bullet is carrying some heat along with it.
The cartridge cases are nice and warm as they build up around your legs when blasting away (M2 and MK19). Your SAW is throwing them elsewhere.
Much of the propellant gas mass is being sent somewhere else too.
Face of the bolt and firing pin are absorbing some of the heat/energy as well.

The chamber/barrel are not the only heat sinks.