Shooting Guns In Space

I was asked a question recently about shooting a firearm in space, specifically on the Moon but we’ll treat it as space generally and hit some specifics about the moon that are different. We’ll focus on normal “Earth guns”. That is guns that are designed to work on planet Earth within all of the environmental conditions present on the planet.

Shooting in space generally:
We’re going to ignore things like calibre, bullet weight and velocity and just focus on the most trivial bits here first. Shooting a pistol in space would probably not be very mundane but for a few microseconds if we assume that the weapon isn’t exposed to direct sunlight. It could get downright deadly to the shooter though. Space is not just big but super cold. It’s about the coldest environment you could think of. Not much of anything in the universe is much colder, especially if the sun isn’t shining directly on you. Assuming that it’s not then the gun is going to be something crazy like -400 degrees F and change.

At these kinds of temperatures the metal in the gun itself would tend to be very brittle and upon firing it would almost certainly explode unless made from an alloy designed to be flogged near absolute zero. The exploding pieces would be moving at approximately 2/3 of the burn rate of the powder and would certainly wound, if not chew up very badly, the astronaut as well as his space suit so he’d be hurt generally and exposed to the vacuum of space in short order and have his blood likely sucked from his body from any holes that managed to get poked in his skin. Perfect way to ruin a space suit and a day and a pistol.

If the gun was not in the shadow but instead exposed to the sunlight then the side of it that’s lit would rapidly heat while the other side soaks the heat. This would result in some parts of the gun reaching over 200 degrees Fahrenheit and other parts reaching -200 until equilibrium was reached. There’s no air in space so the cool side of the gun wouldn’t conduct and transfer the heat effectively to anything else which means the whole gun will soon be ridiculously hot. This will almost certainly cause malfunctions of the mechanism. Some parts would swell while others might contract. Slide rails and cylinder hands and all the little bits inside the gun that fit so tightly would begin to fit too tightly or not tightly enough and there’s a strong probability that the gun just would not fire. If it did fire there’s a near certainty of some kind of malfunction for anything semi-auto. Revolvers would probably fare pretty well though and single shots might be physically unaffected depending on how robustly they’re constructed.

If it did fire while sizzling hot then the ammo is going to be hot from baking in the chamber and you’re going to find a dangerously overpressure round as your first one and they’ll get worse as you keep (if you can) firing. Eventually you’ll see a kaboom and the brass case will open up and things will get 20 kinds of bad suddenly, very similarly to shooting the gun when it’s -450F and it explodes but this will be higher energy but also probably less destructive to the shooter. Metal is still pretty darned strong when heated to modest temps of a few hundred degrees and so the gun probably wouldn’t explode so much as you’d see the mag launched from the gun, the slide stop broken, a burst cartridge case and that sort of thing. The same sort of thing you’d see from a kaboom on a range on Earth. For a revolver, a loose cylinder gap could be utilized to accommodate the potential for large over-pressures.

Special ammo could be created that’s ultra-high temp compatible but because space is burning hot in the light and freezing cold in the shadow it would almost certainly be either very inconsistent or not very powerful. If something isn’t consistent you don’t want to make it very powerful. Makes hiding from the blast when necessary a harder thing to identify as being necessary.

There’s also the problem of inertia. In space proper, you hold a pistol and shoot directly away from you. Well, unless you’re braced against something that can provide counter thrust then you’re going to be pushed backwards away from the direction the bullet was launched. The bullet will continue forever in a straight line until acted on by a force like gravity or impacting something. So will the shooter. The bullet will move hugely fast but you will not unless the gun you were using was a howitzer. You’ll move backwards from your firing position at a speed relative to the total energy being projected. The bullet will get half and you’ll get half. So if the bullet has 300lbs/ft/sec of energy, so will you and you’ll move away at a speed reflective of that input energy which would be fairly slow even by terrestrial standards.

Shooting On The Moon:
So we’ve dealt with the bits of shooting while floating in space which is where the danger really resides. All of those problems are present on the moon. Light at 250F and dark at -400F is one thing. Micro-gravity is another problem of its own.

Apart from the fact that shooting a firearm on the moon would be a violation of international treaty it could be pretty dangerous too depending on the gun. Since gravity is weaker there the bullet will drop slower meaning if you’re not careful about weapon and ammo selection you might just shoot forward away from yourself and end up with the bullet hitting yourself in the back a few hours later. That would require a nasty fast bullet and is really borderline hyperbole but it’s still potentially true. The bullet’s maximum horizontal range – the distance it travels before gravity pulls it to the ground – is given by the equation:

R = v2 × sin (2a) / g

g is a measure of the strength of gravity. On Earth, it is 9.8 m/s/s. To find g on the Moon, we need another equation:

g = G×M/R2

G is the gravitational constant, M is the mass of the Moon, and R is the radius of the Moon. So, on the Moon:

g = 1.6 m/s2

Acceleration of gravity on earth is 9.81m/s/s. On the Moon it’s 1.622m/s/s. On earth with air resistance a bullet leaving at 3K fps will slow to 1.5K fps by .7KM and will have been flying for about one second meaning it’s fallen 9.81m (darn near 30 feet). On the moon it’d not slow down due to air resistance because there is none and so would fly at 3K fps (~1KM/sec) until acted on by something else to slow it down.

The moon being 10K and change kilometers around a bullet would need 10K and change seconds of flight time to make it around the Moon and hit you in the back if launched at 3K fps. This means that you’d have to launch the bullet from an altitude of over 1.6kilometers and then nearly 3 hours later be standing on the surface to get hit. Like I said, it’s possible technically. The bullet would not fling off into space. Even if you shoot it vertically, it’ll probably still be captured by the Moon’s gravity and eventually return instead of zinging across the solar system.

Truth be told, ballistics on the Moon is massively simple compared to ballistics on the Earth. The Moon rotates on its axis so slowly that vertical coriolis drift are essentially non-factors. Spin drift would also be reduced or nearly eliminated. Horizontal Coriolis drift would continue to be a problem because the Moon is still not a cylinder but instead an oblate spheroid. That makes it so there are really no straight lines when you engage in free flight over the surface. When you fire a gun on the surface of the moon you might get scooted back a tad from where you were standing but not far because there is some gravity there. Just enough gravity to be useful.

Once you’ve made it past the temperature and gravitational effects and the lack of atmospheric drag you get to the other problem: What the hell are you shooting at. There’s nobody there gunna rob you and you can be certain that if you leave your shit there that it will definitely not get stolen. There is also a distinct lack of any sanctioned firing range so the target practice excuse kinda kicks its legs up and dies.

Shooting on the Moon brings with it nearly all the problems of shooting in space (all of them that are problems because of a lack of gravity) and brings with it brand new problems unique to an environment with some gravity, though not much, and with all of the problems of heat/cold and a lacking atmosphere. The benefits of no atmosphere are to be had too. Consider what would happen to a groundhog on the moon if hit by a bullet from 10K kilometers away that was still going 3K fps. You think they fly into the air when hit with a .223 bullet still doing 2K fps after flying 400yrds across a field in South Dakota, wait’ll you see how high they fly when you hit them at 3Kfps from 10,000,000 yards and change. Betcha that surprises the shit out of them.

The ideal gun to shoot in space would be the Gyrojet. The projectiles fired are actually rockets and don’t have a lot of initial thrust (takes a few feet to get really sizzling) so recoil would be minimal and because they’re rockets meant to burn over a respectable amount of time instead of powder meant to burn more or less all at once the shooter is unlikely to be sent whizzing in the opposite direction with much energy.

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