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Spudguns in space

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Spudguns in space

Unread postAuthor: Demon » Sat Nov 21, 2009 9:58 am

Just for fun ;

What would happen if we would be firing a steel QEV airgun in a no-pressure environment( such as a vacuum chamber or in space ) ?
The gun would be loaded before getting in outer space or the vacuum chamber.

Would it make the gun gain extra power or blow up? ?
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Re: Spudguns in space

Unread postAuthor: Ragnarok » Sat Nov 21, 2009 10:07 am

Demon wrote:Would it make the gun gain extra power or blow up? ?

Increased power. We already know this, as many research guns use evacuated bores to increase efficiency.

Curiously, there was a discussion on a similar note in the Spud Chat a while ago, but about regular firearms in space. The conclusion was that while they could fire, without air to help cool them, the heat from sustained fire would destroy the firearm.

And on the note of the Spud Chat, last night we worked out that any Tennis Ball launcher which genuinely had a mile range would, due to the drag a) immolate the tennis ball from sheer velocity and b) be capable of taking out a modern battle tank at short range.
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Unread postAuthor: CpTn_lAw » Sat Nov 21, 2009 10:13 am

You would have to pressurize it less, take into account that in space, there is no (in fact, extremely little and thus negligible) pressure. So the moment you depressurize your airlock, relative pressure will rise. If we put aside all of these little problems... shooting in space would be fun i guess...but since you would fly in the opposite direction quite fast (depending on your cannon's size).
Our projectiles velocities are no where near "space like" velocities... So, i guess it wouldn't be as fun as one would think...But a railgun in space would make some cool light effects :D
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Unread postAuthor: jrrdw » Sat Nov 21, 2009 11:14 am

There is all ready a vacuum asisst launcher here but I can't remember the name or builder. Do a search for it you might get lucky and find it quickly.
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Re: Spudguns in space

Unread postAuthor: D_Hall » Sat Nov 21, 2009 12:10 pm

Ragnarok wrote:Curiously, there was a discussion on a similar note in the Spud Chat a while ago, but about regular firearms in space. The conclusion was that while they could fire, without air to help cool them, the heat from sustained fire would destroy the firearm.

Ignition COULD be a problem.

Nitrocellulose really doesn't like to burn at low pressures. IF the air inside the cartridge escaped(*) and the cartridge was at a low volumetric loading, there's a very real chance that the primer would go... And then nothing. If you're lucky the bullet would exit the barrel at some very low speed. If you're not lucky the bullet would get stuck in the barrel.

That said, IF the air remains inside the cartridge or the volumetric loading is high it should work just fine.

As for sustained fire.... Many variables. Radiative cooling is certainly a possibility and one that is used without issue on the nozzle skirts of MANY rocket motors in space. It depends on what you define as "sustained", the materials your gun is made of, and the safety margins thereof.




(*) Cartridges are typically water tight. Does that make them air tight? Not necessarily. I'm not saying they aren't. I'm saying that without more data it's hard to definitively say.
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Unread postAuthor: ThegunGuy » Sat Nov 21, 2009 1:05 pm

I reload cartridges and if you add primer sealer and use a taper crimp it will be air tight. When I first started reloading I added primer sealer to soon and could see the bubbles of air leaking out of the primer pocket, It turns out when you reload a pistol cartridge it can generate up to 20 psi or so from the bullet seating. If I had added primer sealer and let it dry the cartridge would have held the pressure.
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Unread postAuthor: john bunsenburner » Sat Nov 21, 2009 2:44 pm

The awsome thing in space would be that you could hit targets 100miles away and hit perfectly if you aimed properly, technically you could fire a spud across the universe... haha...if we could fire a spud faster than the universe expands then we could have a spud, from a spud gun, be the first object to leave out universe...

Another fun part would be that you would be pushed in the opposite direction with the same force your projectile has...it would be really fun!
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Re: Spudguns in space

Unread postAuthor: Ragnarok » Sat Nov 21, 2009 2:45 pm

D_Hall wrote:Radiative cooling is certainly a possibility and one that is used without issue on the nozzle skirts of MANY rocket motors in space.

I'd already done some calculations to that effect. Typical firearms barrels are not designed in such a way they can lose the energies involved via radiative cooling.
Although I only did rough calculations, "combat use" of most assault rifles would probably take the rifling out within a few minutes.

It does depend on how you choose to define "destroyed", but I'd personally consider something with the rifling stripped out, even if it will still fire, to be rather "ronnied".

Nitrocellulose really doesn't like to burn at low pressures.

True, but the air pressure in the cartridge should be negligible compared to the pressures created by the primer.

Obviously, we'd need experimental data to know for sure, but my guess would be it would ignite.
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Unread postAuthor: jackssmirkingrevenge » Sat Nov 21, 2009 3:17 pm

The damn Ruskies certainly thought it was feasible.

I would imagine the biggest advantage of a spudgun in space would be the lack of air resistance, finally claims of shooting over a mile would be credible :)
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Unread postAuthor: Ragnarok » Sat Nov 21, 2009 3:41 pm

jackssmirkingrevenge wrote:...finally claims of shooting over a mile would be credible :)

Well, with that in mind, the reduced gravity (or lack of, depending on where you are) and extreme launch height would help as well.

Also, as far as I understood, the TP-82 was largely for survival after landing back on earth. I can't see much reason for firing it in space...
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Re: Spudguns in space

Unread postAuthor: D_Hall » Sat Nov 21, 2009 4:29 pm

Ragnarok wrote:Although I only did rough calculations, "combat use" of most assault rifles would probably take the rifling out within a few minutes.

I'm not aware that many soldiers carry enough ammunition to shoot continuously for a "few minutes." Figure a M-16 shoots at 800 rpm. Figure a soldier carries half a dozen 30 round clips. That's about 14 seconds worth.

True, but the air pressure in the cartridge should be negligible compared to the pressures created by the primer.

Obviously, we'd need experimental data to know for sure, but my guess would be it would ignite.

Agree, but my point is that it's not a given. I know the hobby rocketry guys don't use NC for their pyro charges at high altitude because it's very difficult to ignite in a meaningful way, but I acknowledge that's a different scenario.
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Last edited by D_Hall on Sat Nov 21, 2009 4:40 pm, edited 1 time in total.
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Unread postAuthor: jeepkahn » Sat Nov 21, 2009 4:31 pm

jrrdw wrote:There is all ready a vacuum asisst launcher here but I can't remember the name or builder. Do a search for it you might get lucky and find it quickly.


ahem...cough...<looks>....

I'm the one that raved about vacuum assist a ways back, never got to do any empirical testing(my compressor was a loaner and went away) and my vacuum pump is an aspirator type that requires compressed air...

But I can tell you that it makes a huge differance with light projectiles and a considerable differance with heavier ones, I had some theories back then, and since have reassessed some of them and I believe I've settled on the fact they make more differance than just the added 14.7psi differance between atm and vacuum is that the vacuum changes the internal flow characteristics and raises the internal mach # and expansion rate of the pressurized gases... But until I actually get another compressor and do the testing, it's just a theory...
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Unread postAuthor: D_Hall » Sat Nov 21, 2009 4:43 pm

jeepkahn wrote:But I can tell you that it makes a huge differance with light projectiles and a considerable differance with heavier ones, I had some theories back then, and since have reassessed some of them and I believe I've settled on the fact they make more differance than just the added 14.7psi differance between atm and vacuum is that the vacuum changes the internal flow characteristics and raises the internal mach # and expansion rate of the pressurized gases... But until I actually get another compressor and do the testing, it's just a theory...

Having run "real" laboratory guns with vacuum on the barrels I'll say that the difference in performance is absolutely trivial to calculate for supersonic guns.

Shoot without vacuum. Measure muzzle velocity. OK....

Let:

Mp = mass of projectile
Ma = mass of air in barrel
Vb = baseline velocity (shot with air in barrel)
Vv = velocity with vacuum in barrel

The energy of the system is very nearly constant (makes sense since your power source hasn't changed).

What you find is that...

Mp * Vb^2 = (Mp + Ma) * Vv^2
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Unread postAuthor: Brian the brain » Sat Nov 21, 2009 4:46 pm

Now why hasn't anybody thought of the fact it can be extremely cold out there?


For those with PVC cannons:
Please don't go and shoot it in space... :roll:

We have enough space debris already..


Back down to earth:
If I would create a vacume in a barrel, I would need to seal the muzzle.
Preferably with something like a plastic bag or aluminium foil burst disc.

Imagine the projectile going ( past) the SOS..
The projectile still has to break the seal...wouldn't that take it right back down below SOS?

If not...I'm goin for it!...well...someday...
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Re: Spudguns in space

Unread postAuthor: Ragnarok » Sat Nov 21, 2009 4:54 pm

D_Hall wrote:I'm not aware that many soldiers carry enough ammunition to shoot continuously for a "few minutes."

I didn't say they were firing continuously. I'm talking about use as if they were in combat - a few minutes of use of the firearm as would be expected under those conditions would be about enough to require the barrel to be replaced.

Figure a soldier carries half a dozen 30 round clips.

That sounds on the low side. I know when I was in Army Cadets that my webbing had the pouches to carry a dozen magazines (not that the bastards ever gave me that much ammo), so I'd expect that carrying ~500 rounds is normal enough for soldiers.
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