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Firing Modern Day Guns in Space


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#1 Orpheus

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Posted 19 January 2003 - 11:36 AM

In my misspent youth, I knew my way around guns and explosives. But it's been a long time, and the one thing I learned back then is that three afficianados in one room = an argument. Sometimes it originates from ignorance of basic physics; often, it originates in bad information in seemingly reliable sources; and when all else fails, there's always *some* oddball example that seem to break the rules.

For this reason, I generally avoid such discussions,and prefer to do my own research on subjects that will plae my neck on the line. However, since fiction rarely kills, I offer the follwing observartions with caveat that the are entirely broad generalities.

How strictly are we interpreting "modern day gun"? I presume that we aren't literally firing a centuries-old museum piece. I've seen, firsthand, some pretty spectacular failures of guns just a century or so old. I'd wager that the metalurgy and quality control of the better made firearms are substantially superior today to the guns of a century ago, but most guns in general circulation in the US today are no-names; some so cheaply produced that it's remarkable they can be safely fired at all -- amd some can't.

With a few modifications, however, todays basic designs can operate quite well in space.

FIRING IN A VACCUM
A modern chambered cartridge can fire in a vacuum. The chamber/cartridge + barrel + projectile must be a substantially airtight system for a gun to operate well. Substantial leaks would allow the propulsive gases to escape, decreasing efficiency, and releasing hot corrosive gas that would be dangerous or uncomfortable to the operator. It would also be instantly visible as a flash in unexpected places on the gun. Small chamber flashes, for example can sometimes be seen on (e.g.) poorly maintained or badly designed guns.

Control of exhaust gas (incl .blowback mechanisms, anti-recoil ports, flash ports, etc.) is a major element of gun design, generally so fundamental that the end user rarely has to worry about it. Even ammo feed takes a backseat -- many guns have problems with ammo jamming, but a semi-auto with *any* problem with exhaust gases shouldn't make it off the drawing board (in an ideal world)

Since the cartridge is sealed to gegin with, and the cartridge/barrel/projectile create a *largely* sealed system while the projectile is in the barrel, no air from the external environment participates in the reaction. If anything, the muzzle velocity and range would be significantly greater in a vacuum. (subject ot constraints below)

You can readily demonstrate that bullets will 'fire', by impact or electrically, underwater. However, I would not suggest using a gun for the test. Water in the barrel and mechanism would make this very risky for both the gun and firer.

CARTRIDGE FAILURE IN VACUUM
Modern off-the-shelf cartridges might have problems with "unseating' of the projectile in a vacuum, especially in the larger calibers, due to the way cartridges are made. As the projectile is seated in the cartridge, the air in the cartridge (initially at 14.7 psi) can be compressed to 100 psi or more (Keep in mind that the powder in the chamber represents almost incompressible deadspace: If you have .95 cc of powder in a 2cc chamber, and you seat the projectile until the there is only 1 cc of space in he chamber, the internal pressure would be 1.05/.05 = 21 atm = 309 psi!

Therefore, a .45 caliber round with an effective transverse rear surface area of about .16 sq in could experience an 'unseating force' of 15-50 lbs. Sudden depressurization of such a cartridge could cause the projectile to dislodge slightly or pop off the cartridge entirely, preventing proper firing. The first round might be ineffective, because its projectile might be halfway up the barrel (creating, in effect, a giant chamber with very low initial chamber pressure, and little propulsive force) or might have popped out of the gun altogether. Subsequent rounds could easily jam, because they are no longer the spec length, even if they stay 'in one piece'. This applies to both revolvers and semis

A cartridge designed for "space use" (i.e. packed at a vacuum or low pressure) would operate equally well in a vacuum or an atmosphere. The heating of air trapped in the cartridge is a minor effect, with probably a net negative impact on muzzle velocity.

SEMI-AUTO vs. REVOLVER
Crudely put, a semi-automatic firearm uses the recoil or blowback gas from the discharge of one cartridge to load and chamber the next cartridge. A revolver generally has several cartridges, each pre-loaded in its own chamber, and uses the first stage of the trigger pull to rotate a new chamber into place. Revolvers are considered somewhat more reliable by most, but clearly semi-autos [e.g. any gun with an ammo clip) are more popular. To round out the picture, a full-auto (e.g. machine gun) simply takes the semi-auto one step further, and triggers the firing pin as long as the trigger is still depressed.

Clearly exhaust gas handling, cartridge unseating, etc. would be more crucial in a semi-auto, so they would benefit from a slight redesign for space use. The difference would not be noticeable to any user, but it would spell the difference between something that 'might work' and a reliable weapon.

VACUUM WELDING, THERMOMECHANICAL EFFECTS
Guns and cartridges made for space use would probably have alloys and coating to prevent vacuum welding and other effects in the mechanism, chamber, cartridge etc. A TwenCen museum piece stored in a vaccum might not be operational after a few years or centuries in a vaccum.

Many parts on a stock modern gun are probably sensitive to cryogenic effects, but they don't need to be. Lubricants would freeze. Firing pins or chambers might shatter. Barrels might contract or warp out of spec, etc. Again, proper choice of design and material can fix all these problems, most likely with little change to the design. It's mostly a matter of testing, rather than redesign. However, under susteained fire, chambers can get quite hot, and thermal effects creep in that would make the gun fail, or be less durable.

PROPELLANTS AT CRYOGENIC CONDITIONS
Don't assume that propellants would work less well at cryogenic temperatures. Ordinary wood briefly soaked in liquid oxygen can produce a fairly decent explosive (Don't try this at home, kiddies!) Liquified gases have different properties and reactions, and may actually produce dangerously over-powered chamber explosions (another argument for vacuum-packed cartidges in space) especially after extended cryogenic storage. Reformulated (or space-tested) propellants would be much safer than current ones.

It is worth noting that a gun in a pocket or box, even an external pocket of a space suit would not rapidly cool to cryogenic temperatures. After the initial decompression, it would only cool by radiation abd conduction, and an object in a small enclosed space would radiate to the walls fo the space (which would also re-radiate back to the gun)

CONCLUSION
I would guess that if we tested the provided scenario in space today, the gun would fire in a high percentage of trials. In other space-based scenarios, the reliability and safety might plummet, but I can see no impediment to the operation of substantially modern design in space, with some design mods and testing.


#2 Christopher

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Posted 20 January 2003 - 09:09 AM

On the hull breach issue, I'm not sure it's that great a concern.  Remember, space is full of micrometeoroids, and spaceships tend to move very fast.  Micrometes would often hit with at least as much kinetic energy as a bullet.  So if possible, spaceship hulls would be designed to be able to withstand such impacts.  I believe some proposals call for an aerogel layer -- an incredibly light, foamy material that can snag the projectiles, absorbing their kinetic energy (like the way a foam bicycle helmet absorbs the energy of impact by deforming, only much more so), but which is also such a good insulator that it easily dissipates the resultant heat energy.  If it would keep micrometes from penetrating inward, it would presumably stop bullets from penetrating outward.  Another approach would be a sealant -- even if you can't stop the projectile from penetrating, you could include a hull layer that would leak an expanding, quick-hardening sealant into the breach and close it up before more than a little air was lost.  (This sort of thing was seen in Malcolm Reed's spacesuit in the Enterprise episode "Minefield," though one has to wonder why the spacesuits from two centuries later don't have it.)  So unless you're talking some kind of armor-piercing shell, I think the decompression risk is manageable assuming the hull construction is reasonably advanced.  At least, the only way in which the risk from bullets is greater than the risk from meteoroids is probability -- a ship is a small target in the vastness of space, but a bullet fired from inside can't miss it.
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#3 Orpheus

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Posted 20 January 2003 - 05:32 PM

You might not even have to go high tech.

Rearward vented exhaust ports near the barrel tip woul allow  exhaust gas to counteract much of the recoil (this is done today) True, it wouldn't be an exact countermatch, but if you can't take  *any* momentum hit, you'd run if he started flinging boogers.


#4 Rhea

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Posted 27 January 2003 - 06:09 PM

Orpheus, on Jan. 19 2003,16:36, said:

However, since fiction rarely kills, I offer the follwing observartions with caveat that the are entirely broad generalities.
ROTFL!

Are you COMPLETELY sure about this?  :devil:

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#5 Robert Hewitt Wolfe

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Posted 19 January 2003 - 03:00 AM

Reposting from the Science in SFTV thread:

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The other thing that they did was admit that they needed oxygen to fire a projectile from one of Jayne's guns in space, and so, used a spacesuit.  

This one is interesting.   I did some research about whether or not a modern firearm would, in fact, fire in vacuum for my unproduced feature ZERO GEE.  From what I remember, I got a "probably" from the people I talked to.  The oxygen is inside the shell casing after all (chemically incorporated into the explosive charge), and that's sealed.  So the precussion should still set it off.

The bigger problem, from what I remember, was the cold.  I vaguely remember a discussion about whether or not the gun would freeze up before it could be fired.  

The problem is, though I remember the discussions, I don't really remember the conclusion.

Let me go check:

+rummages around in his files+

Ah, here it is:

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EXT. SPACE - CLARK’S P.O.V. - NIGHT

A spacesuited figure floating in the void, holding a pistol.  The pistol’s muzzle flashes again, propelling the figure backward and sending a bullet straight at Clark.

So... I had the pistol fire in vacuum, but only in a situation where it had recently been in a warm, pressurized environment.  Oh, and the scene takes place on the dayside of earth, so there's sunlight to keep things warm.  

Now, the question is... was I wrong?  Or was I right?  Because... as I start to recall... I remember having an entirely different solution involving an O2 tank and some plastic bags if I need the O2, but I was told I didn't.

Opinions?

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#6 Christopher

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Posted 19 January 2003 - 09:22 AM

Great to see you here, Robert!

Sid's right about heat loss in space: you'll lose heat faster in a 5-degree atmosphere than in a minus-270-degree vacuum, because conduction and convection are more efficient than radiation.  Indeed, in the sunlight you'd have to worry about overheating.

One thing I have to ask, though...

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EXT. SPACE - CLARK’S P.O.V. - NIGHT

"Night?"  How can you tell, if they're in space?  :D

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#7 CJ AEGIS

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Posted 19 January 2003 - 12:45 PM

Interesting posts.  The two big concerns I can think of right offhand would be recoil and getting the right level of penetration without having too much.  Don’t want to blow through the side of your own vessel if you fire it inside.  Yet you also don’t want to have your frangible rounds stopped by light weight body armor.  

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Orpheus: some so cheaply produced that it's remarkable they can be safely fired at all -- amd some can't.
Cough Glock! Cough

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#8 CJ AEGIS

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Posted 20 January 2003 - 12:23 AM

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Robert Hewitt Wolfe : It would probably be smart to carry two different kinds of ammo, too.  Flechettes or something without a lot of punch for use inside, something with more power for use outside.

Flechettes might do the trick depending on their penetrating power.  I’m not exactly up on small arms frangible rounds and instead end up thinking of their larger tank-busting brethren.   The big problem with frangible rounds is a good heavy leather jacket would make adequate body armor against them if you were more than a few arms lengths away.  Toss in some Kevlar, other protection, and you have some pretty good body armor against them.  Not exactly great to be worrying about dieing from a hull breach and instead get killed by an enemy your guns can’t harm.

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#9 Orpheus

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Posted 20 January 2003 - 10:32 AM

Alas, I got called away from the Keyboard before posting.

I was in the process of composing a reply that now only confirms Christopher's point:

While I agree that a 'hull breach' is nothing to be trifled with, I think that the danger from internal small-arms fire is overstated, especially in the context of a mature space technology. We endure far greater potential risks in our daily lives: e.g. one gallon of burning or exploding gasoline has a potential lethality well over 10kg of TNT, yet through proper design, we all routinely drive around with 5-10 gal in our tanks, and lethal fires or explosions are rare.

A 5.6mm (.22 caliber) round leaves a hole of under 25 sq. mm (millionths of a sq meter) and would leak roughly 10-12 L of 'standard Earth atmosphere' per second. Does that sound unreasonable? Perform the following experiment:

1) Make an enemy (Optional. Will be handled by step 3 anyway)
2) Sneak out to your enemy's car late at night and measure the width, inner and outer radius, temperature, and air pressure [typically 29-44 psi or 2-3 atm) of their tires.
3) Snip off a tire valve, creating a roughly .22 sized aperture for the air to escape. Measure the time it takes the tire to deflate (several seconds) Repeat x3.
4) Sneak home and calculate the estimated rate of depressurization.

The muzzle velocity of a .22/5.6mm *rifle* is ca. 500 m/sec (.5 km/sec). Handguns have much lower muzzle velocities, are rarely discharged inside a ship, and leave small punctures. By contrast, space debris ranges from orbital velocities (1-10 km/s or more) to relativistic velocities during travel (100,000-300,000 km/sec),comes in a variety of sizes, and are encountered every minute of the life of the spaceframe. Damage to a ship is proportional to the mass but the *square* of impact velocity.

Even the mildest enemy ship-based assault (e.g. the nose mounted .50 'gats' that five year old Al Capone XXXVII and Eliot Ness XXXVI have on their zero G Big Wheel replicas at Perseid Orbital Day Care Center #16675) will generate 1000x the damage of a handgun round. A "real" space weapon wouldn't even be comparable.

The real danger would be to important shipboard systems (regional processors, C5I, the Captain), not tiny hull breaches, and would likewise be routinely dealt with by routine repair, redundancy and other design considerations, as part of routine spaceworthiness.


#10 CJ AEGIS

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Posted 20 January 2003 - 02:41 PM

Interesting.  So it guess it would only pose a threat to very early generation craft.  

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Orpheus: The muzzle velocity of a .22/5.6mm *rifle* is ca. 500 m/sec (.5 km/sec).

Something like 850 m/sec for a M-16 though you are dealing with a 5.56 mm in that case.  

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Handguns have much lower muzzle velocities, are rarely discharged inside a ship, and leave small punctures.
ca. 350 m/s for a M9 9mm Berretta IIRC.

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#11 jon3831

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Posted 20 January 2003 - 05:06 PM

Robert Hewitt Wolfe, on Jan. 20 2003,04:08, said:

Seems foolish, and in space, foolish people would tend to die, IMO.
That little maxim applies just as well right here on earth... Usually the one to win a gunfight is the one who makes the fewest mistakes. But I digress...

One concern that I would have is the recoil. We can absorb recoil on the ground 'cause we have gravity and friction working on our side. With a Zero-G environment, it's concievable that the shooter would have neither, and the discharge would act like a thruster...

(Of course, this could be dealt with by automatically stabilizing thruster packs, but that takes the fun out of the discussion ;) )

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#12 Ro-Astarte

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Posted 20 January 2003 - 06:00 PM

Orpheus, on Jan. 20 2003,22:32, said:

... but if you can't take  *any* momentum hit, you'd run if he started flinging boogers.
:oops: Then again, who wouldn't flee from space boogers?  :alien:

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#13 CJ AEGIS

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Posted 21 January 2003 - 12:11 AM

jon3831, on Jan. 20 2003,22:06, said:

One concern that I would have is the recoil.
Wait simple go for a real hand howitzer... :devil:  Ah a nice M1911A1 in space.....  :wideeyed:

Quote

After that, distance really wouldn't be an issue, as you'd be likely looking at some mighty good increases in stopping power in a vacuum.

Of course without that pesky issue of extra weight bothering you one could really go crazy on body armor.

"History has proven too often and too recently that the nation which relaxes its defenses invites attack."
        -Fleet Admiral Nimitz
"Their sailors say they should have flight pay and sub pay both -- they're in the air half the time, under the water the other half""
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#14 Uncle Sid

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Posted 19 January 2003 - 03:51 AM

After looking some things up, you're right as far as I can tell.  If a gun uses modern ammunition were the bullet caps off the explosive charge which is in a brass casing (or whatever), you should be able to fire it in vacuum.  Since just about every gun that I can think of uses that kind of ammo these days (and presumably 500 years from now),  there should have been no reason that they couldn't fire that weapon in space, except maybe for the heat issue.  In fact, as it has been pointed out by others, since there is no air in space, the heat from a weapon would have to cool by radiation, which is much slower.   Thus the weapon would probably not freeze immediately, even without the sun available to heat it up.

Now, they were firing the weapon from Serenity in what seemed to be deep space, so temperature might be a concern, but as I recall I believe that oxygen was mentioned as the problem.  

I'll have to go back and review that episode.   It's possible for some strange reason that the weapon in question was using a non-standard round where oxygen might be a concern, but that wasn't how the scene played out in my head, and so it would be a ret-con, at best.  

Err...and uhh....  Hi Robert!  
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#15 Robert Hewitt Wolfe

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Posted 19 January 2003 - 11:08 PM

Christopher, on Jan. 19 2003,14:22, said:

Quote

Quote

EXT. SPACE - CLARK’S P.O.V. - NIGHT

"Night?"  How can you tell, if they're in space?  :D

:p We never specified "Day" or "Night" in space on Andromeda or DS9, but it looks weird in a feature script not to do one or the other, so I arbitrarily labelled the spacewalks "Night" and the interiors "Day" or "Night" depending on the station clock.

Thanks for all the feedback, all.  Awesome article, Orpheus.  Glad to know I didn't blow it.  Now that I know we basically got it right, I'll credit Paul Woodmansee for talking me through this the first time through and setting me on the right path.

Just FYI, the gun in this case was a semi-automatic pistol, not purpose-built for use in vacuum.  

Now I find mysedlf wondering what the hell any good spacer (as in the FIREFLY example) is doing carrying a weapon that isn't 100% reliable in vacuum or pressure?  Seems foolish, and in space, foolish people would tend to die, IMO.  It would probably be smart to carry two different kinds of ammo, too.  Flechettes or something without a lot of punch for use inside, something with more power for use outside.

And to go back to the original post about Science in SF TV, I do beleive thinking about these kinds of things and at least trying to get them right is the only smart way to proceed with an SF show.  Whether you get things right or wrong, I believe the audience can tell when you're at least trying.  And as long as you keep trying to make things believeable, why shouldn't they keep trying to believe them?

Later.

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#16 Ro-Astarte

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Posted 20 January 2003 - 03:09 PM

Robert Hewitt Wolfe, on Jan. 20 2003,04:08, said:

Now I find mysedlf wondering what the hell any good spacer (as in the FIREFLY example) is doing carrying a weapon that isn't 100% reliable in vacuum or pressure?  Seems foolish, and in space, foolish people would tend to die, IMO.  It would probably be smart to carry two different kinds of ammo, too.  Flechettes or something without a lot of punch for use inside, something with more power for use outside.
While I agree with your point overall, Jayne (the Firefly character in question) had a freakin' arsenal in his bunk of both edged and projectile weapons.  "Vera" was just his "favorite".

So, in that case I can see the combination of distance and vacuum being an issue. That was a looooong shot to make.

Or am I retconning through my butt here? I haven't shot a weapon in some time, and then it was only a 22 rifle.

Ro-Astarte


#17 Jid

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Posted 20 January 2003 - 10:36 PM

Astarte, on Jan. 20 2003,14:09, said:

So, in that case I can see the combination of distance and vacuum being an issue. That was a looooong shot to make.
Actually, the biggest problem I can see with a distance shot in space would be the royal pain in the butt of having to resight in your rifle for a zero-G environment.  (Sighting in while in Gravity implicitly negates gravity's effects, but in Zero G, you'd begin to shoot high at an appreciably short distance without some form of recalibration.)

After that, distance really wouldn't be an issue, as you'd be likely looking at some mighty good increases in stopping power in a vacuum.

YMMV of course.

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#18 Etude in E

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Posted 31 January 2003 - 01:25 PM

So, if you do shoot a gun in space and you miss your target, how far will the bullet go?

#19 Ro-Astarte

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Posted 31 January 2003 - 03:25 PM

Well, no friction, right? So it just becomes another microparticle (is that the right term?) of space flotsam until captured by a stronger gravity.

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#20 Nick

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Posted 13 February 2003 - 10:35 PM

Wouldn't firing any projectile sufficiently fast in space present a major safety hazard?  I don't know any of the numbers--but the whole equal/opposite reaction thing might become an irritant, as the murderous spacewalker flies back at at least a few meters per second after firing . . . seems like they'd need some clever propulsion packs to compensate for kickback.

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