Would a gun work in space?

[Zeriel]

@EdIsenberg

I won’t keep repeating myself for your entire response, because you make statements without any citation, and without responding with why you feel my remarks are incorrect. I do want to point out your statement quoted above.

The reason a gun can explode in outer space or on The Moon is due to different expansion and contraction of the bullet, the cartridge casing, and the barrel of the gun. Since on Earth we don’t have such a different temperature between sunlight and shadow (or day and night), the expansion & contraction doesn’t have much effect, and are well within the tolerances of the gun and ammunition specifications.

I looked this up a bit:

Copper = 0.016mm/m per degK
416 Stainless = 0.010mm/m per degK
Various Lead Alloys = around 0.028mm/m per degK

So if there’s going to be a problem, it’ll be in the bullet itself. The worst problem that can happen with the casing is that the gun will jam or improperly feed, and in that case it won’t explode anyway. So let’s take a common military caliber: 5.56×45mm NATO

The Earth-nominal diameter for the bullet itself is 5.7mm (or 0.0057m) @68 degF (293 degK).
By your cite, the nominal black-body temperature of an object in space will end up at 394 degK–a difference of 101 degK. We’ll use that number since it gives us the greatest temperature difference likely to be in play.
With that difference in temperature, you’d expect to see the bullet expand by 0.00571010.028 = 0.000016m, or 0.016mm, an increase of 0.28%.
In the same heat, the barrel expands by 0.00571010.010 = 0.0000057m, or 0.0057mm, an increase of 0.10%

The difference in the two diameter increases is 0.010mm

So the question then becomes, “Is a typical rifle capable of dealing with being 0.010mm out of tolerance without exploding?” I don’t honestly know the answer to this question, and I can’t find one in limited googling. Given, however, that I know people who routinely feed 5.56x45mm through .223 Remington rifles and vice-versa (the latter case makes me be very far away just in case they are unclear on the pressure differences from the powder loads, granted), I expect the answer to be “yes”–especially since the ANSI B4.1 tolerance grade 8 (the highest generally specified for “boring” operations like machining a rifle barrel) is 0.0177mm or thereabouts.

Now, if they’re using diamond-drill boring for those gun barrels or a different process altogether, then we can talk, but right now I’m personally comfortable with “won’t explode”.

I’m also willing to bet that, given the relative speed of conduction in metal vs. radiation received in terms of transferring heat, the situation where part of a gun is in sunlight and part is in shadow is not especially relevant.

[chorpler]

@EdIsenberg

Don’t ask what would happen to an astronaut with a dozen holes in his/her space suit and, under that, a dozen holes in his/her body. It is very grisly.

Please, tell us what would happen – I’m interested to hear what your opinion on the subject is. From the research I’ve seen, it doesn’t appear to be that grisly, but you may have different sources.

[Chronos]

To be fair, an astronaut pumped full of holes would be considerably grislier than an astronaut exposed to vacuum without extra holes, or a person pumped full of holes in Earth-normal atmosphere.

[chorpler]

Well my question isn’t limited to EdIsenberg. Can you explain the details?

(I mean, assuming you’re talking about something more grisly than just “there’s extra blood coming out of the holes,” which it sounds like you are since you specified that it would be more grisly than in an Earth-normal atmosphere.) Exposed fluids will boil in a vacuum, but I’m assuming there’s more to making it grisly than just clouds of blood vapor.

In my experience, posters like Chronos and science fiction authors like EdIsenberg are usually pretty good at describing things like this and backing them up with cites, so I’m anxious to learn, even if it is somewhat disturbing.

[Chronos]

You’d bleed out faster in vacuum than in atmosphere, and any blood that shot out would just keep on going out, in zero-g. And personally, I think that clouds of boiling blood would be plenty grisly enough, thank you very much.

[chorpler]

@Chronos

You’d bleed out faster in vacuum than in atmosphere, and any blood that shot out would just keep on going out, in zero-g. And personally, I think that clouds of boiling blood would be plenty grisly enough, thank you very much.

Heh heh … oh, sure, grisly enough, but compared to the effects in Outland or Total Recall, it’s pretty tame … and those people hadn’t even been punched full of holes.

[penumbrage]

@Allston

After a bit of thought, one further post (then I’ll shut the hell up!):

Modern propellants are designed to have a specific burn rate within atmosphere (performance X, between Y bars and Z bars of atmospheric pressure). With no atmosphere, your burn is very different, and unless you’re postulating the chamber of a firearm is a totally sealed environment, you will experience a large gas loss. Most propellants are approximately 20% oxidizer, but taken as with any equation, the presence of atmosphere is a distinct part of it. It may even be opaque to most, e.g. not mentioned, but it’s there nonetheless. In short, a huge decrease in gas-pressure by which to propel your round.

[Different skew if this is not an automatic, of course]

Seems to work OK (in near vacuum).

Ignoring the irrelevant gunpowder analysis, nitrocellulose with 8 oxygen atoms burns well in an inert atmosphere or a vacuum.

Seemed to work OK for the Russians (in hard vacuum).
Salyut-3 (OPS-2) space station.
Admittedly, I have no idea what modifications were made to the 23mm Nudelman-Rikhter automatic cannon or it’s ammo.

The major difference in internal ballistics is not having to compress and expel a column of air in the barrel ahead of the bullet. While this does mean the burning curve of the powder will be less than ideal, peak chamber pressure happens early in the bullet’s trip down the barrel while peak air column resistance happens towards the end, so only the last half of the bullet’s acceleration curve will be significantly changed.
While you could optimize the burn curve for space (and get better than atmospheric performance) it’s still a fast and effective projectile with which the space hero can dispatch baddies.

[Quercus]

I hope I’m not piling on here, but I wonder about a few of these.

@EdIsenberg

The impact of the gun hitting the shooter’s helmet might even leave a serious crack, so that the shooter dies both from decompression and oxygen-starvation.

Anyone with any training in firing a gun will brace it against themselves, so there is no sharp impact; and in particular, guns are not usually held so that the stock impacts the shooter’s face.

@EdIsenberg

If you are on The Moon, with only one-sixth Earth gravity, firing two shots in quick succession will result in the second shot going wild.

I’m not so sure about this. The muzzle of a gun fired on Earth rises because the gun is generally held on the lower side, and the recoil makes the whole gun rotate around the support point. On the Moon, a shooter doesn’t need to support as much weight, so they’ll be able to hold the gun with more even pressure on the top and bottom sides, so muzzle rise will be less (assuming, though, that the weight of the shooter is still enough to keep the shooter from moving significantly with the recoil).

@EdIsenberg

In zero or microgravity (not the same) or even on a low-gravity environment like The Moon, the recoil from a gun aimed by sight will make the shooter tumble backwards head-over heels. It will also apply some thrust to the shooter, so that he/she will be thrust backward in space. There is no easy recovery when this happens, and when multiple shots are fired from the eye of the shooter, the tumbling can cause all the blood to run to his/her feet, making the shooter pass out and even die of oxygen-starvation to the brain.

Now, the point about torque from the recoil causing tumbling is a good one. But I’m a little dubious about the tumbling being able to black out the astronaut. I can stand on my head, or hang upside down for reasonable amounts of time without passing out, so one gee of acceleration is bearable.

If I haven’t screwed up the math, for a (tall) 2 meter person spinning around their midpoint, it takes a spin of 8 revolutions per second to create a one gee acceleration at the tip of their head.

And, using an astronaut of 75 kg (light, considering the suit needs to be included), and assuming a uniform mass distribution, I think (probably with a math error here) that an 8 Hertz tumble needs 6,400 Joules of kinetic energy, which is it appears less than a .50 caliber round, but needs three or four M-16 rounds. Since, unless you’re braced against something, more energy is going to go towards linear backwards movement than tumbling, I think it would be hard to make yourself pass out by firing bullets in zero-G and causing yourself to spin.

Just trying to help in case any of your upcoming stories have this as a plot element. You know how science fiction fans are about accuracy.

[Irishman]

@Quercus

Anyone with any training in firing a gun will brace it against themselves, so there is no sharp impact; and in particular, guns are not usually held so that the stock impacts the shooter’s face.

At least with the right experience. I recall shooting skeet once where I gave myself a black eye from gun impacting my face due to trying to look down the barrel for aiming. Unfamiliar gun, not much experience.

I’m not so sure about this. The muzzle of a gun fired on Earth rises because the gun is generally held on the lower side, and the recoil makes the whole gun rotate around the support point.

Technically, the issue is that the line of action of the momentum from the bullet is above the line of action of the bracing - whether that is a pistol holding the grip below the chamber, or a rifle or shotgun with the stock against the shoulder. You are correct that part of the problem is the shooter is fighting gravity to support the gun until firing, but the real cause of the recoil shifting the barrel direction is the misalignment between the recoil and the support. If a handgun were built with the supports equally bracing the top and bottom and braced directly behind the barrel, that would not occur. (Well, autos/semi-autos with cartridge discharge would have a twist from the shell ejection, but the barrel wouldn’t “walk up”.)

But I think you are correct that on the Moon, the shooter could expend more strength balancing the bracing rather than supporting the weight, and control the recoil more tightly. But he might have to widen his stance a bit or something because his own traction is a bit less.

In weightlessness, the shooter is going to want some sort of stabilization and recoil prevention, or else the first shot will send him spinning. Not enough to black out or probably not injure himself, but enough to make semi-auto or autofire useless if not hazardous.

[penumbrage]

You should be fine on the moon with just a wider stance (insert Sen. Craig joke here). You have the same mass to absorb the recoil, the only change is that the force required to push your center of gravity past the edges of your boots has been reduced to 1/6th.
If you need to have your hero shoot (or vector his thrust) accurately and repeatedly in zero gee, just have him brace his laser sighted firearm just above his waist, perpendicular to and at his center of gravity (your hero having practiced this technique to perfection in case his life depended on it).
Since Irishman is right, muzzle rise is designed into Earth guns (the recoil thrust line is always placed above the center of the grips or shoulder pad), the hero should cancel out this resulting angular momentum by rotating the weapon 180 degrees every other shot for relatively stable thrust.
His velocity and radial spin (imparted from revving the bullet to 50,000RPM) can be canceled with matching shots at the same CG but from the small of the back, either immediately (to stay stable for the rest of the gunfight) or after flying back to safety from certain death.
Just remember when using your MMU (munitions maneuvering unit) that your ride home may not be bulletproof.