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Water-Injected Machine Gun

Boost the bullet and cool the barrel at the same time.
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So, take a .50cal. The bullet spends about 1ms in the barrel. This is long time. Especially in the days of electronics. F1 engines (before the rule changes) span up to 22,000 RPM. Their fuel injectors open and close wonderfully quickly... so that they can be pretty accurate down to micro seconds. Now, you fire a standard round. This is sensed, and a water injector, modeled on a piezo- electric fuel injector adds atomized, purified water immediately after the bullet passes. This changes heat into additional pressure.

The main limiting factor for the firing rates on machine guns is heat. Existing solutions include multiple barrels, or simply swapping the existing barrel out. This goes someway toward replacing that. Additional force is added to the projectile, which may allow for a smaller charge for the same overall range/penetrative power.

bs0u0155, Aug 01 2012

The Puckle Gun http://en.wikipedia...le_gun#Two_versions
Be there, or be Square ... [8th of 7, Aug 01 2012]

Wikipedia on Vulcan Cannon http://en.wikipedia.../wiki/Vulcan_cannon
I found the word "fuzeless" interesting in context of the conteporaneous HB discussion on varian English spellings. Maybe to distinguish from "fussless"? [bungston, Aug 02 2012]

[link]






       Do I get a cookie for seeing the immediately after?
Voice, Aug 01 2012
  

       go on then. Call it editorial pay...
bs0u0155, Aug 01 2012
  

       // This changes heat into additional pressure. //   

       To be accurate, it uses heat in the propellant gases to vapourize water, theoretically increasing the pressure but lowering the temperature.   

       // The main limiting factor for the firing rates on machine guns is heat. //   

       No, it isn't. It's ammunition supply.   

       // Additional force is added to the projectile, which may allow for a smaller charge for the same overall range/penetrative power. //   

       Thermodynamically, it should deliver improved efficiency.   

       BUT ...   

       The breech pressures in a gun barrel are orders of magnitude higher than those in an internal combustion engine.   

       Most modern weapons are gas-operated. This will result in high pressure steam being introduced though the gas port into the gas piston system, which is quite a lot cooler than the barrel.   

       It will emulsify any lubricant present in the piston chamber, and it will also condense, eventually resulting in water being reinjected into the barrel on the piston's return stroke as a new round is chambered; water in a gun barrel ahead of a high velocity round is a Bad Thing.   

       You're adding a layer of complexity to an already complex device; and it requires electrical power, too.   

       You need to carry a supply, albeit a small one, of water. Water's heavy. You've already got to lug the weapon, ammo, cleaning kit, and yourself around. It's just another extra little burden.   

       The only people liable to be toting purified water around a battlefield are the medics.   

       Plus for ingenious thinking, but sadly impractical.
8th of 7, Aug 01 2012
  

       Why not just have a small pad of water-rich gel on the back end of the bullet?
MaxwellBuchanan, Aug 01 2012
  

       i) The less water in a gun barrel, the better.   

       ii) the gel would have to be partitioned off from the propellant with 100% reliability; the rough handling ammunition undergoes, not least in the feed process itself, needs to be factored in. Accelerations are considerable.   

       iii) The mass of the gel would have to deliver more in terms of increased projectile velocity than an equivalent mass of propellant.   

       iv) the complexity increases the cost of manufacture.
8th of 7, Aug 01 2012
  

       Yes, but apart from that?
MaxwellBuchanan, Aug 01 2012
  

       Apart from that, and   

       <Placeholder for extremely long-winded and abstruse discourse on the many negative qualities of this idea, which may well form the basis of a series of advanced lectures at the Royal Military Academy Sandhurst on the topic of "It Seemed Like A Good Idea At The Time">   

       it's clearly the greatest "advance" in gas-expansion projectile weapons since James Puckle mooted the idea of using a gun firing square bullets for use against infidels ...   

       <link>
8th of 7, Aug 01 2012
  

       I have only one thing to add, and that is: damn, the Borg beat me to it.
Alterother, Aug 01 2012
  

       [+] Oh cannonbollocks.   

       I wouldn't worry too much about condensation in the barrel: gunpowder produces water too and at 600rpm there isn't enough time to form droplets big enough to mess with a lead bullet.   

       Likewise putting a valve in the gas cylinder that expels the return stroke air is pretty easy.   

       Emulsification might be a problem but when was the last time you heard of a .50cal going on vacation just because it was raining out.   

       The injection point would have to be before the bullet goes supersonic, but after the flamefront had passed, of course.
FlyingToaster, Aug 01 2012
  

       Elmusification would not be an issue, in my view. I think the Borg pulled that one out of their collective asses to round off the argument. They are quite right on all other counts, however.   

       Furthermore, the injection would have to take place at the breech, not in the chamber. This raises two problems:   

       4) the injection port adds volume to the barrel, so the propellant gasses will have more room to fill and thus will transfer less energy. This also entails a re-design of the barrel, since assymmetrical forces will now by exerted around the area of the port.   

       #A) the injectors, as my esteemed colleague(s) collectively pointed out, will have to exert a phenomenal amount of pressure to add anything to that already present. What they omitted, however, was the consequence of failure: the explosive force that should be pushing the bullet down the barrel will instead be exhausted via the injector and, assuming in this case that 'hilarity' is synonymous to 'high- velocity shrapnel', hilarity will ensue.
Alterother, Aug 01 2012
  

       x) the actual problem would be trying to find a location in the barrel where you could inject water after the flamefront had passed (so you don't quench the propellant) but before the bullet goes supersonic (so the pressure wave can catch it and push).   

       Yes, the barrel would have to be strengthened simply to make up for the fact that somebody's taken out some of its substance to put an injector in there.
FlyingToaster, Aug 01 2012
  

       So, diesel engines get peak pressures of around 300 Bar. .50 cal get 3-4000 bar. Not a world away, and direct injection diesel engines have injection pressures of 1000 Bar. We're pretty close in the grand scheme of things. I'm not too worried about reliability either... direct injection engines have expected lifespans MUCH longer than any rifle/gun. So I think the injectors will be fine.   

       Barrels do overheat. I understand that Gatling- type weapons use multiple barrels for simultaneous loading-firing-ejection.... however the rotating barrels represent forced air cooling... it's mentioned in Wikipedia on either rotary cannons or Gatling guns. The British Army GPMG is/was specced for barrel swap every 5-600 rounds. I'm told that the swapping time can feel like hours in the field!   

       I suspect that water might not be a problem if it's designed into the weapon from the get go. There are plenty of weapons designed for all- weather/semi submersed. However, the point is phase-change expansion.... the working fluid can be any number of liquids. Water's super handy and RO purification is available in many military vehicles.   

       The weight argument's not valid.... the use of water increases the efficiency of projectile propulsion. A smaller charge is needed for the same effect. For the same amount of kinetic energy contained within the projectile, the Water system should be lighter.   

       The electrical system will be necessary, only for the piezo/sensor setup, . So it's not for the common assault rifle.... think bigger: squad level .50 cal > 30mm cannon > 80mm > naval guns > satellite launch guns.   

       As for the on-the-back-of-the-bullet idea, are there any solids that would sublimate at the appropriate temperatures?
bs0u0155, Aug 01 2012
  

       //any solids that would sublimate at the appropriate temperatures   

       I do seem to recollect one person fooling around with plastic fibre, to pack out the cartridge case, to keep a very reduced load of propellant next to the primer, and it being burnt up totally due to the heat in the barrel, and so not leaving a load of residue.   

       I can't remember why they wanted to do this though.
not_morrison_rm, Aug 02 2012
  

       also water injection would reduce muzzle flash..
bs0u0155, Aug 02 2012
  

       To be honest, you'd be better off doing he whole thing with LPG.   

       Incidentally, if the injected water radically reduces gas temperature and so the pressure for the mechanism, you could then use a larger ptfe piston and so not have provide oil for it.
not_morrison_rm, Aug 02 2012
  

       //        The weight argument's not valid.... the use of water increases the efficiency of projectile propulsion. A smaller charge is needed for the same effect. For the same amount of kinetic energy contained within the projectile, the Water system should be lighter.    //   

       Care to cite a reference stating that steam has greater propellant force than cordite, please? Pound for pound, powder's got more bang, friend.
Alterother, Aug 02 2012
  

       Why are you injecting water, rather than, say, petrol/gasoline?
hippo, Aug 02 2012
  

       Most likely, a clear but unstated ambition to live to see another sunrise.
8th of 7, Aug 02 2012
  

       //Care to cite a reference stating that steam has greater propellant force than cordite, please? Pound for pound, powder's got more bang, friend.//   

       It's a basic assumption of the idea that adding water will increase the pressure.
I don't see how that works but 8/7 has already passed this, and IIRC some car engines do it, so presumably there's some basis in fact.
  

       Given that, suppose one aims to keep the pressure the same by using less explosive and replacing the weight with water. It is possible that the water will have a higher mass than the explosive removed. In that case it would at least have the advantage of reducing the explosive needed, which might be a benefit if in short supply.   

       However, it seems to me that water isn't a brilliant substance to use. High specific heat capacity, high latent heat of evaporation - it's great for sinking heat, but crap for producing pressure. Hence I'd have thought that hot gas would have more pressure than gas + steam. I suspect the benefit where water injection is used is that there is a high temperature bound; one can provide a higher pressure at this maximum operating temperature by using more fuel but converting excess heat into pressure.   

       Perhaps instead of water, one could find a substance to replace some or all of the cartridge casing? You would want something solid, sturdy and inflammable, but which would sublime to produce copious gas at high temperature and pressure.
Loris, Aug 02 2012
  

       //Most likely, a clear but unstated ambition to live to see another sunrise.// - but apart from that? Actually what I meant was: You can build engines which operate safely, and which you inject petrol into, so why not a gun barrel? It might not be practical, for all sorts of reasons, but is might be possible.
hippo, Aug 02 2012
  

       //   It is possible that the water will have a higher mass than the explosive removed. //   

       Not 'possible', certain.   

       // advantage of reducing the explosive needed //   

       <pedantry> the contents of a cartridge are propellants, not explosives </pedantry> please forgive.   

       // one could find a substance to replace some or all of the cartridge casing //   

       Baked; see 'caseless rounds'. They met with limited popularity, used with innovative guns like the G11 and a rare P90 variant.
Alterother, Aug 02 2012
  

       //<pedantry> the contents of a cartridge are propellants, not explosives </pedantry> please forgive.//   

       While I welcome your pedantry, I would suggest that most propellants are in fact also explosives. I concede that there may be non-explosive propellants, such as compressed gas, but they would presumably not heat up the gun, rather the reverse.
Which does suggest another avenue - a small chamber of compressed gas, released during barrel transit, to both increase propulsion and cool the gun.
  

       //Baked; see 'caseless rounds'.//   

       The wikipedia article ("caseless ammunition") makes no mention of a cooling effect. There are two things which make me think what I proposed is not part of their design.
Firstly, they are described as "a solid mass of propellant ... cast into shape to form the body of the cartridge". This is not the same as having an explosive part and an evaporating part.
Secondly, there is a section on "heat sensitivity" of caseless ammunition. Basically they will ignite themselves if the gun is too hot. If they were as I described, the gun would not get as hot, and a round in a hot gun would lose coating (cooling its surroundings) rather than firing.
  

       Incidentally I'm not claiming either of these as genius ideas - I can think of several potential drawbacks with both.
Loris, Aug 02 2012
  

       Adding fuel to the whole scenario gets messy. It doesn't trade heat-for-volume in the same way.... well, it might, initially, but should the barrel conditions be sufficiently anoxic, you'll expel a cloud of flammable vapor... which will, at some point either burn or explode in a manner most inconvenient.   

       From what I can tell, explosives have an expansion ratio of about 1000:1. Whereas the water > steam expansion is about 1600:1.. what I was trying to create was a bit of an explosive powered steam- engine hybrid.
bs0u0155, Aug 02 2012
  

       // While I welcome your pedantry, I would suggest that most propellants are in fact also explosives //   

       <UberPedant>   

       No.   

       There are strict technical definitions about what are combustibles, pyrotechnic mixtures, deflagrants, propellants and explosives.   

       Propellants are very specifically NOT explosives. They are characterised by subsonic propagation of the flame front through the composition, and propagation by thermal transfer rather than hot particles. In explosives, the process of detonation is mediated by a supersonic shock wave causing decomposition of the material.   

       Most detonating high explosives burn quite slowly with a yellow, sooty flame when ignited in air. Some formulations won't burn at all, they just melt. Propellants have a very noticeable tendency to "flash" on ignition, known as the "say goodbye to your eyebrows" effect.   

       </UberPedant>   

       [bs0u0155], you're right about the superior expansion of water. But this has been extensively researched, and if there was a practical benefit and it could be done, it would have been done by now.   

       Infantry weapons and their ammunition need to be as light and portable as possible consistent with being rugged, reliable and simple. The water-cooled Vickers guns of WW1 needed a 5-man team to transport and operate them. It's just possible, with practice, to fire a GPMG from the hip.   

       At any semi-fixed location - on a vehicle, an aircraft, a ship - water cooling is available for barrels.   

       Another big issue would be ammunition interworkability. The ammunition would have to be useable in every weapon of that calibre in the inventory. Otherwise, if there's a mix-up, disaster beckons, and if there's one thing that's certain to occur on a battlefield it's muddle and mix-up.
8th of 7, Aug 02 2012
  

       I'm not sure. This is certainly Half-Baked, but seems to be submitted as an actual advance, so I will judge it as such.   

       There is a rather serious point that this wouldn't work for two reasons. Water injection in cars does not add power in itself, it raises the effective octane rating by slowing the flame front propagation which allows active timing systems to advance timing and thus resulting in a longer power pulse. It does this by injecting the water in at MUCH higher pressures than the ambient intake airstream to allow for good atomization. So expect to require a magnitude larger pressure than what exists in the barrel or the water will not vaporize, or it will not have any effect on the gas pressure, but I would say that the only effect that this would have is to delay the pressure pulse. So what you would need to make this work beside some type of railgun style injector is to rework the charge completely to increase it's strength under the plan that the initial pulse will be dampened by the water injection and we are relying on the increased pressure later in the cycle to make up for initial losses.   

       Hmmm. Does qualify for [8th]s reckless use of explosives and it does have that whimsical nature that we don't know who the gun will kill, the shooter or the target, but in the end I have to go with (-).
MisterQED, Aug 02 2012
  

       gaah! it's like significant improvements to mature technology is difficult or something!!!
bs0u0155, Aug 02 2012
  

       but interesting discussion. Re mature technology, after the detained dismissal of the idea 8th mentions that water cooling is in fact available for fixed location guns. I would be interested to know how cooling is actually achieved for something like a shipboard Vulcan cannon.
bungston, Aug 02 2012
  

       //if there was a practical benefit and it could be done, it would have been done by now.   

       Oh, how I wish that was true..please forgive a mini-recap as we have been over some similar territory before.   

       1944 someone in the German Army realises that on an actual battlefield, in rainy north Europe, you are very unlikely to even be able to see the enemy one mile away, so pretty pointless having a big heavy rifle, with big heavy cartridges, and so the assault rifle was born. About 20 years later, someone in the American Army realises exactly the same thing....they set up a (presumably) incredibly long-winded research program (the Salvo study) and so the M16 is born.   

       The problem is the military structure, society has two basic large organisational structures, the business model and a political model. This a third kind of structure. It has no profit motive, generals are never recruited from outside, the soldiers don't get to vote on who is the most effective general etc It's a structure guaranteed to promote a lack of progressive thinking.   

       End of mini-rant.   

       If you could use holy water it might come in handy for campaigns in the Carpathians?
not_morrison_rm, Aug 02 2012
  

       //No.
[...]//
  

       Thank you for a most enlightening correction.
Could I interest you in correcting the wikipedia "caseless ammunition" article, which refers to "a non-crystalline explosive"?
Loris, Aug 02 2012
  

       "explosive" is one of those words with a slidey meaning depending on context and audience. When you hear about gasoline or gunpowder "exploding" it's the container that does the exploding, not the substance. The difference between "FOOM" and "BOOM" as it were.   

       Note that the article uses the word "propellant" five times and "explosive" once (and that in close proximity to the company name "Dynamit Nobel"). So yes, the WP article is (probably) wrong, though maybe the company salts the propellant with a bit of detonant for more equal burning or something.   

       [edit: the "non-crystalline explosive" is probably polynitropolyphenylene, used both as a binder and a velocity-modifier for the propellant... (way out of my depth here: see new post "Armchair Podium")]
FlyingToaster, Aug 02 2012
  

       //No. [...]//   

       Was that a general no, or no to specific point, I'm just curious.
not_morrison_rm, Aug 05 2012
  

       I've toyed with the idea of having coolant in the actual cartridge behind the propellant of an exact amount necessary to remove the heat caused by that one shot. I dumped the idea because the amount of coolant necessary was huge so your cartridges would be about five or ten times the size and heavy as hell.   

       I saw a continuous firing ceramic barrel machine gun where the guy just sat there for a minute unloading rounds. That would seem to be the way to go. Let me see if I can find the link.
doctorremulac3, Aug 05 2012
  

       // Was that a general no, or no to specific point, I'm just curious. //   

       It was a very specific and pedantic "No".   

       //polynitropolyphenylene //   

       Close, but no cigar. But yes, you're on the right track - you need to research "active binder technology" just a bit further. Not all of it's on the web, yet.   

       // Let me see if I can find the link. //   

       Damn, did we leave that up ?
8th of 7, Aug 05 2012
  

       Seriously, can't find it. Did I just dream that? Sounds like the kind of dream I'd have.
doctorremulac3, Aug 06 2012
  
      
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