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Cool Guns for your Games


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9mm vs. ballistic gelatin:      

Most people.      Meanwhile, at the other end of the spectrum, environmentally conscious autoduelling:    

Not really a gun, but ammo for one   New Drone-40 grenade/drone. Launches out of a 40mm grenade launcher, but has a drone function that they claim can loiter up to 20 minutes, has different

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This looks to be an 8" barreled SBR built around The 15th Upper/Lower receivers by Hera Arms, a Hera Arms 7.5" rail, the Hera Arms CQR stock and CQR foregrip, a Magpul PMAG D-60 drum, an Eotech optic, and Troy BUIS.  Overall a very attractive CQB AR-15 ... as well as a poster child for AR-15 accessories by Hera Arms.  However, a space gun ... it isn't; you could build this today. :)

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I thought the point was that it would work in space.  ;)

 

 

Well any gun past 1880 or so will work in space.  Bullets will fire in a vacuum, and even travel a little bit faster.

 

 

Yup. As long as they fire from a sealed cartridge, they will fire.

Firing more than a couple of times might be iffy, though. Heat build up would be a major problem.

 

Gunpowder requires oxygen to burn.  Modern cartridges contain their own oxidizers, so guns that use modern cartridges CAN be fired in space.  However, it would be anything but fun (given Newton's 3rd Law)...

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What is the thermal release of a (e.g.) 7.62 mm cartridge? You have me thinking about cooling systems.

This is an interesting question -- one I can't readily answer.  I would expect that the thermal release would depend on a] how many grains of powder were used in the load; b] how much nitrocellulose was used in the powder; and c] the precise oxidizers and amounts of them within the powder.

 

That said, I don't think the issue would be with heat produced from the rounds, themselves, but rather, from the heat from rounds when combined with radiation exposure from a nearby star.  Imagine a firearm in the hands of an astronaut in high Earth orbit as the sun hits the astronaut's suit and the firearm.  The barrel and chamber of the firearm will go from a chilly -100C in the shade of Earth ... to 120C in full sunlight.  It isn't instantaneous, but this ~220C temperature change takes place.

 

At 120C (248F), the barrel and chamber will be more than halfway to the 400F mark generally required to cook off rounds.  It won't take many rounds to hit 400F ... especially if the firearm is suppressed...

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Actually, even if you're in complete shadow a gun would overheat very quickly if used. Vacuum is the best insulator - the heat from each round would stay in the metal elements of the gun. It would take very little to get up to gang-fire temperatures, and after that all your gun would be good for is ballast.

If it got that far. If you've allowed your weapon to cool to ambient space temperature without stellar radiation, you're talking about a massive thermal imbalance between the expanding gases and the metal...which has chilled to well below it's brittling point. Likeliest result would be the entire weapon shattering into shrapnel - in your hands. Your spacesuit covered hands...

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Radiative warming and cooling I know to compute; that's pretty easy. And frankly the heating can be minimized with some simple shielding. I can estimate the frictional heating generated by the bullet being spun up by the rifling (in vacuum you may not need the rifling, but it may still be the easiest way to keep the slug sliding rather than bouncing down the barrel, which is what limited the accuracy of the old smoothbore cannons), though I expect that's small compared to the heat of burning of the propellant, which I expect to be enormous compared to the KE imparted to the projectile. Some of that will get consumed in the adiabatic cooling of the propellant gases, but again I expect only a small amount.

 

But as Surrealone said, I don't have a good idea what the propellant heat is, though given an hour or so I could scratch up a crude estimate.

 

I'm inclined to think that your space gun will need a cooling system. Just making **** up out of my head, maybe a circulating-liquid system around the chamber, with the coolant forced through a refrigerator where the heat is taken up by the expansion of a high-pressure inert gas that is released about the same time as the propellant fires. In other words, your gun is double barreled and has a dual munition, one to throw the bullet, the other to provide a heat sink. Again, I'd have to push numbers around to see what order of magnitude you'd need.

 

EDIT: it wasn't until after I posted the above that I realized that I had converted the "Cool" in the thread title from an adjective to a verb.

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And how long the water jacket would remain servably full after you filled it. Hours (at minimum) would be needed for that to work operationally. Unlike the terrestrial water-cooled .30 Browning, in space, you can't just drop your pants and urinate in the cooling radiator if your water runs low.

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Actually, even if you're in complete shadow a gun would overheat very quickly if used. Vacuum is the best insulator - the heat from each round would stay in the metal elements of the gun.

 

This is true, it would start out insanely cold but warm up very rapidly and stay that way because there's nothing to take the heat away.  You'd need something.  A recycling water system would only work until the water was all superheated.

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Yes you could build it today but I will Ment that a props guy for a sci-fi movie would slap some LEDs on it and call it good like the P90 and the Tavor. http://www.imfdb.org/wiki/FN_P90

 

http://www.syfy.com/sites/syfy/files/styles/syfy_image_gallery_full_breakpoints_theme_syfy_smartphone_1x/public/2016/07/Killjoys_gallery_203Recap_10.jpg?itok=XviRKoz6

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