How do guns work in space?

[Video Link] Important questions in physics, explored by vsauce. This one will come in handy for those of you headed to Mars for target practice. The ballistics specifics start around 4:00 in.


  1. He doesn’t even talk about how the bullet doesn’t need oxygen or more heat to fire. That’s what I’m always concerned about. If a bullet is in vacuum at near to absolute zero will it fire.
    And will the extra pressure in the barrel make it pop ?

    1. They did mention that modern gunpowder has it’s own oxidizer.
      The ignition of the gunpowder would generate the heat.
      A gun barrel is designed to resist the interior pressure, there wouldn’t be excess pressure, there would be less pressure on the outside of the barrel.

      1. Materials behave very differently at extreme temperatures as compared to room temperature.  Remember when Mr. Wizard dipped that racket ball in liquid nitrogen?  The ductile bouncy ball became as brittle as break away glass.

        If you were in direct sunlight the heat might ignite the gunpowder in the shade the gun would probably explode.

    2. compare to an OMS burn.  the fuel-ox mixture used self-ignites when combined, producing thrust.  thrusters essentially turn a spacecraft into a large, slow-moving bullet.  the only difference is that ammunition must be struck to initiate the reaction.
      in space, a gun does make noise, but this is only audible to the person holding the gun. nobody else present could hear it, as there is no medium to convey the sound wave from the weapon to another person unless they are also in physical contact with the gun or the shooter.

  2. Uhm, this is all basic ballistics, in space!

    Nothing about firing off conventional firearms “in space”(and/or in environments not usual in comparison to the earth).

    1. Then you learned wrong.  I was floored by the silliness of the scene in one episode where Jayne had to find a space suite to put around his rifle so that it would fire, the incorrect assumption being that firearms require air to fire.  They don’t.  If the “sub-aqua” version of the Glock will fire underwater, then it should be pretty clear that atmospheric oxygen isn’t necessary to the process.

      That was the only moment in an episode of Firefly that was so idiotically wrong in a violating-the-laws-of-physics way that I couldn’t suspend disbelief and just enjoy the episode as a whole.  That’s a big deal for a total fanboi who’s perfectly willing to accept even a visual as ridiculous as cows milling about in the hold of a spaceship as a part of the story and still be willing to enjoy the show.

      1. Thermal control does matter, I’d be rather nervous about using a “normal” gun at +-200 degrees centigrade. Low temps I’d worry about the steel getting brittle (and the powder will burn slower, resulting in a lower velocity bullet), higher you might have your ammunition cook off, and the powder will burn faster, resulting in higher pressures. Even mill spec isn’t rated that high temp. 

        Also, in prolonged vacuum, you may have lubrication issues.

      2. Maybe he was trying to prevent the moving parts from cold-welding together when they rubbed off their oxide layers? Or the action involves a piston dampened by outside air in the cylinder?

        Something about that scene seems like a conscious choice, they specified that “Vera” needs air around her to fire, not guns in general. I want to believe…

        1. Yeah, I want to believe, too.  But Vera was AK-based and they could have survived the scenario with just one shot.

          Still, I wanna believe sooooo bad…

      3.  I experienced similar disappointment, but it did not stop me from enjoying that episode.  Christina Hendricks!

        I just sort of learned that I had to turn science off if I wanted to enjoy Firefly, and I’m glad I did!

        1. It’s unnecessary to specifically invoke Ms. Hendricks when providing a reason to enjoy Firefly.  If you want to go down that path, *any* of the recurring female characters could provide overwhelming motivation.

      4. If the “sub-aqua” version of the Glock will fire underwater, then it should be pretty clear that atmospheric oxygen isn’t necessary to the process.

        I can’t see how those would be related. Surface tension would handily maintain an air bubble in a sloppily sealed container underwater. The vacuum of space is less forgiving. Particularly since the cold of space is going to alter the size of both the slug and the casing, affecting the seal.

        1. Hmmm.  You might be right in that the harsher environment and the vacuum of space might compromise the seal between bullet and case; and between primer and case.  (I’m granting this for the sake of a productive discussion but I don’t really believe it.  I’ve sealed lots of bullets and primers in cases using both mechanical means and chemicals.  I know from experience that those tiny brass bottles are mighty tough little containers.)  But what difference does that make?  Primers produce spark due to a chemical reaction not requiring gaseous oxygen to be present.  That would ignite the gunpowder which will burn just fine in a vacuum, releasing the large quantities of gases that push bullets out of barrels.  Are you working under the mistaken assumption that gunpowder has some problem burning in a vacuum?  That’s not the case, as several folks have already pointed out.  Or are you thinking that the vacuum and temperature extremes of space might cause a catastrophic failure of the cartridge to hang together, i.e. as soon as the cartridge is in a vacuum, the bullet and primer will just slide right out of their respective ends of the case?  I find that highly unlikely.  Standard crimping techniques applied to milspec cartridges produce a strong mechanical bond between the components and would likely prevent that sort of failure.  Or are you thinking of some other sort of failure that I haven’t envisioned?

          1. I’m saying that ‘underwater’ and ‘vacuum’ have very little in common and the premise that something will work in space because it works underwater is untrue.

          2. Thanks for clarifying that Antinous.  I agree that ‘underwater’ and ‘vaccum’ have very little in common other than a lack of atmospheric oxygen.

            I also agree that “the premise that something will work in space because it works underwater is untrue.”

            However, I never espoused that premise.  I merely said that one thing the two have in common (the lack of atmospheric oxygen) is no hindrance to firearm function.

            Given that, I really have no idea what you’re on about. 

            Please don’t feel under any obligation to explain.  I’m probably just being thickheaded due to lack of sleep.  I think I’ll retire for the night.

        2. Actually one of the real problems that would face a firearm in space isn’t just cold, it’s also heat. With no air there’s no cooling available other than black body radiation, which is a much slower way to shed heat than convection and conduction through air. A metal object in direct sunlight at the Earth’s distance from the Sun can get up past 200 degrees F. Those kinds of temperatures could start to affect a firearm’s function.

          There’s a reason almost everything on the Apollo missions was either white or reflective, it was to try and keep the solar heating to a minimum.

      5. I ask as a someone mostly ignorant of gun matters, doesn’t an automatic weapon such as Vera use air displaced by the bullet to cycle the next round in? Would the gases produced by the explosion of the powder be sufficient?

        I fully recognize this may not apply to all automatic weapons, or maybe just to ancient Sten Guns or something. Happy to learn/be corrected!

        1. Most use gas.  The one used as the basis for Vera does.  Some don’t and simply use the momentum imparted to the system by recoil to operate.

          The gases produced by the powder are enough to operate.  In fact, since there is no air to buffer the movement of certain parts, I can imagine that the mechanism would actually cycle more violently which would tend to make it more reliable in the short term while increasing wear in the long term.

          Ancient Stens are actually quite a bit simpler and would have even fewer issues working in a vacuum.  The same is true of the Uzi I overheated the heck out of yesterday.  Fun day at the range, that was.  :-)

          There are some interesting design challenges to making firearms operate reliably in space.  As noted by others, lubrication could be a problem.  So could excessive heat causing cookoffs.  Regulating the gas system for reliability would require some fine-tuning, certainly.  However, just about any old gun would work in outer space for at least a few shots.  I have no doubt Vera would have worked just fine when exposed to space.

          But that’s not what Jayne said and he should know Vera better than anyone.  Thus, the rapture of disbelief suspension is sadly broken.  Sigh.

  3. The video says to watch another video at the end. That video tells me to go back to the first video. I’m stuck watching these two videos forever!

  4. Guns will work in space— gunpowder has its own oxygen (oxidizer) sealed in behind the bullet.

    The biggest problems for guns in space are:  Recoil (firer flys opposite direction from bullet) and over penetration… nice hole in that thin hull you got there.
    The russians have been sending guns up with their cosmonauts for decades (its a large break open drilling style pistol with two .410 sized shotgun barrels and a 5.45×40 rifle caliber barrel.

    It also has a detachable stock that doubles as a hatchet.
    Their reasoning for the weapon is incase their cosmonauts come down in the soviet far east and have to fight bears, wolves, etc.

    In space they could use the weapon for whatever…. If they fired frangible shotshells and braced themselves against something, it would be a pretty effective weapon.

  5. Newton’s 3rd law, if the bullet is expeled with X amount of force then you will be pushed with the same amount of force in the opposite direction.

  6. This was a reply to CSBD but y’know, disqus.
    I can’t remember it anymore, but I once did the math based on the mass of your standard 5.56 NATO round being fired at the muzzle velocity of an AR-15; If a man of 75kg fired the gun, it wouldn’t impart all that much reverse speed as the  mass of a bullet is so small in comparison to that of the person. Tack on another 100+ kg for a full body space suit and it more than halves that speed. Now rapid fire would naturally add up, but something small like a .223 would probably be easier to use anyway, especially since you’d want to avoid that overpenetration problem you mentioned.

    Edit: I did some napkin calculations, and using 4 grams @ 936 meters/second for the bullet, and 160 kg for the man in a space suit and got circa .026 m/s.

    1. But still, if you were in an EV suit without thrusters an inch per second would put you 100 yards away in an hour if you fired in the wrong direction. Better be latched on or have some thrusters on that suit! (I just love unit calculations)

  7. He’s wrong about the bullet never reaching anything because of the expansion of the universe.
    It’s best to ignore the expansion of space and focus on movement in space. Many stars and galaxies are moving towards us. Andromeda is closing on us at >100 km/s, so it’ll have no problem meeting up with the bullet.

    The real reason the bullet won’t go anywhere is that it lacks the escape velocity. It’ll probably get caught in the Earth or Sun’s  gravity well, since a few mk/s is nothing compared to escape velocities required.

    1. This! I was just about to chime in with it. :)

      At LEO, you need 2-3km/s to break out of Earth’s orbit. And you’d need 42km/s to break out of Sol’s gravity well (given an Earth starting point).

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