Guns in Space
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You are currently reading a thread in /k/ - Weapons
You are currently reading a thread in /k/ - Weapons
How long do you think a conventional automatic rifle (such as the M16A4, which uses 5.56x45mm NATO rounds) could fire in the vacuum of space before heat becomes a limiting factor?
Granted, it's possible the lubrication might freeze before you can fire a shot, so let's assume the gun starts at ambient room temperature. If the round uses 55 grain powder (average amount for a 5.56x45mm) and gunpowder has a specific energy of 3 MJ/kg, then simple math tells us that each round will produce 10.7 kJ of heat (not all of which would be transferred into the gun itself, since energy will be lost propelling the bullet and through gaseous emissions). I'm a bit stumped as to where to go from here, though. I have no idea how hot a M16 (or any other automatic or semi-automatic rifle, for that matter) can get before it locks up. Failure rate is often described in "x failures per 1000 rounds"; I imagine that being air-cooled, you could get through *maybe* a 20 round magazine before heat failure, but that's entirely speculation.
Could someone who knows a bit more about heat management weigh in?
>>29234317
Nigger it's 3am and I've been drinking quit with that shit
In all seriousness though the answer is 4
>>29234317
You also forgot the fact that the casing also helps eject heat
>>29234385
Shit, I should have been more considerate. Sorry everyone.
>>29234403
Ah, right - which would reduce heat even further.
Does anyone know how long you could fire full-auto in normal conditions? It might give some idea as to the upper limit, regardless of atmosphere.
>>29234317
>>29234385
Nigger, I've been drinking too.
And what I think is it wouldn't work too fucking well. The extreme cold, unless you're away from the earth where it's extreme radiative heat, it would probably fuck the gun up, or work just as well.
I would have to look up steel's tendencies in extreme cold, and brass's tendencies in extreme cold, and in a vacuum, and do math.
And nigga I'm way too drunk for that shit right now.
>>29234421
Exactly 6 minutes, 23 seconds.
>>29234317
>>29234429
considering the physics in 0 gravity you're better off with a microwave gun or some other directed energy weapon to defeat alieums if you're in space, tbhfam.
earth guns is for earth niggas.
>>29234436
>fucking melt them instead of punching holes in them with a rock thrower
>this way you don't end up spinning away from your ship for the rest of eternity after a 3rd burst.
>>29234421
This video might be helpful
https://youtu.be/BSizVpfqFtw
>>29234444
I was surprised in the video how it was the barrel that failed before the internal components seized up.
830 rounds before the barrel failed in atmosphere. Well, that's surprisingly more than I expected for a constantly fired automatic rifle. If the barrel was made from 4340 steel, then it had a UTS of 1110 MPa. So by the 830'th round, the barrel had heated up enough to reduce the tensile strength down to a level that the round could punch through - which for a 20" AR-15 would be the 380 MPa of barrel pressure each round exerts.
For 4340 steel, a report by W.J. Trapp Materials Laboratory from 1952 (surprisingly difficult to find more data on tensile strength at varying temperatures) notes that UTS is reduced to 430 MPa at 537 degrees Celsius. If we're generous, we could probably ball-park it and say that barrel failure occurs at around 550 C (since strength would begin to rapidly drop off at this point).
Of course, this doesn't take into account how the stress-strain curve of 4340 changes with respect to temperature, but I'm sure my estimate isn't completely unreasonable.
This is a good upper ceiling for how the gun can perform in a vacuum - no doubt failure would occur much, much sooner. If I knew the mass of the steel components of the gun, I could calculate the direct exchange of heat from the gunpowder and get a better estimation.
>>29234317
You just lub the gun with Krytox type lubricants and use special but simple powder that is resistance to static discharge in a total vacuum. We have gone through all this before....
Heat is not a real problem since you will not fire the gun enough to matter in space. Probably an AK-47 would be best but really any quality gun should do fine.
It's probably not going to be significant, but have you taken radiative heat transfer into account?
>>29234605
Wouldn't you be more concerned with the yield strength than the UTS? Any sort of deformation in the barrel is going to be catastrophic
Doesn't powder need oxygen to burn?
>>29236100
Only black powder does. Modern powders have their own oxidizers.
Would there be an issue with vacuum welds or what ever they are called on the action?
>>29234430
Wrong. It's more like about 3 minutes and 50 seconds
>>29235540
Not only that, but what about softening at temperature? That figure >>29234605 quoted for 4340 is the room temperature UTS, which is useless for this calculation.
JEWS IN SPAAAAAAACE
