So to start things off I know that Compression Rifles work in combat and are deadly. https://en.wikipedia.org/wiki/Girandoni_air_rifle what I'm looking for is a more modern version of the gun, like air-soft or paintball but for military use. Think of a scenario that their was a mass gunpowder shortage and the army had to develop Compression Rifles, how would they design them.

A few of my ideas is that an infantryman would carry around a flamethrower like device or a backpack size one and attach a hose to the gun. Another one is the standard air canister attached to the gun maybe in the stock and reload when the canister runs out. I also would like to know what bullets would be best and what it can fire (explosive rounds armour piercing etc.) and if it can go full auto. I also heard that hydrogen is better than air for gas firing let me know if there are better gases to use. the guns will be for modern use and the full military industry production line dedicated to its production

Here are my two questions

1: What design would be best for mass production in the army?

2: What would be the draw backs in using Compression Rifles in combat?

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    $\begingroup$ You know that mass gunpowder shortage is not feasible, right? You need sulfuric acid, nitro acid and cellulose, basically. If you don't have one of these, your entire industry is pretty much gone. Also, this question is broad and opinion based — best depends on what you want to do with that gun and what you value. Drawbacks of pressure systems are something entire books was written about $\endgroup$
    – Mołot
    Commented Feb 19, 2018 at 17:44
  • $\begingroup$ the gunpowder shortage scenario i used is just to justify using air guns in combat. what i want to do with the gun is give a infantrymen a Compression Rifles and telling him to shoot someone, the Girandoni has proven that you can field the gun in most conditions i just want to know what a modern version would be like. but thank you for the input $\endgroup$ Commented Feb 19, 2018 at 18:07
  • $\begingroup$ Just what infantrymen want: Heavier, requires an additional squad kit to carry the compressor, and shorter effective distance. Drawbacks in combat depend upon the type of combat...though the need to leave your position and return to the compressor every 20-30 rounds is sure a big one! $\endgroup$
    – user535733
    Commented Feb 19, 2018 at 18:18
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    $\begingroup$ Are you targeting a current tech level or something else? I'd expect that before too far in the future you could have miniaturized rail guns. Some of the advantages of a rail gun is relatively simple ammo and few moving parts. $\endgroup$
    – svenvo7
    Commented Feb 19, 2018 at 18:19
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    $\begingroup$ svenvo7 i did ask this question in: Rail-guns designs for hand held rifles and spacecraft. but i found out that Rail-guns would most likely kill the person using it and could only be used with tanks or very heavy sniper rifles $\endgroup$ Commented Feb 20, 2018 at 0:19

2 Answers 2


When you get right down to it, every rifle is really a compression rifle, it's just the storage mechanism of the gas that is fundamentally different.

What gunpowder and other explosives really do is store a massive amount of chemical energy in a small space. Ignition causes rapid oxidisation, and it's the pressure of expanding gases that expels the bullet from a rifle, not the heat. All the heat does is cause the gas to be released / expand.

In that sense, the difference between an air rifle and a 'conventional' rifle is when the gas pressure is created. In a conventional rifle, the gas pressure is created when the bullet is being fired. In a compression rifle, it's created beforehand, stored and released as required.

That means that your air rifle is never going to be as efficient or as powerful as a conventional, gunpowder based weapon. It'll have lower range, less power and more mass than any conventional firearm. There's your disadvantages. But, gunpowder is not the only type of combustion that can cause this effect.

You mentioned Hydrogen gas in your edit. Liquid Hydrogen (and liquid Oxygen) is what they use to launch rockets. NASA uses liquid hydrogen because that packs the fuel in more densely, allowing for the largest possible fuel load. Ignition and oxidisation heats it up VERY quickly, creating very rapid expansion which is funneled out the engine nozzles to produce thrust. (This is a simplification but functionally correct.)

You don't need that kind of power, so why not just put hydrogen gas in a combustion chamber behind a bullet in a gun, and light it?

Even at room temperature, hydrogen gas will explode on ignition, causing a burst of pressure that should be able to fire out a bullet. Hydrogen burns cleanly, creating water (read The Martian by Andy Weir for some fun explanations of playing with hydrogen explosions) and ironically enough, it's simple enough to make as well if you have electricity. You just put a current through water and can break it up into hydrogen and oxygen, which can then be used to fire a bullet, turning it back into water.

In any event, ideally you'd still used pressurised hydrogen to combust so as you get as much pressure behind the bullet as possible, but this could be stored in much smaller cylinders as you wouldn't be storing compressed gas at the height of it's potential energy; you'd be storing a gas, under pressure, which when ignited gives you much MORE pressure. That means your soldiers are carrying around a cylinder of gas, but they get much more bang for their buck (forgive the expression) than they would with conventional compressed air. Certainly enough for a conventional battle.

  • $\begingroup$ Well put, I did think of using Hydrogen for Ignition but I was worried about the production level required would be too great (but since there are no rival compounds like gunpowder) the input would be about the same as powder. Distribution to the front-lines would also be difficult but would carry the same risks as gunpowder. The main problem I see is the like the flamethrower the infantrymen is carrying a potential explosion waiting to happen $\endgroup$ Commented Feb 20, 2018 at 2:46
  • $\begingroup$ Absolutely Creed. Compressed hydrogen is of course very dangerous but then so is gunpowder if mishandled. Flamethrowers come to mind as an analogue in this case, but then it's not the only case where a weapon can be a liability; there's a saying in the military - tracers work both ways. Ultimately it's up to the handlers to use ANY weapon correctly so as to benefit the user to the enemy's detriment. Compressed hydrogen would just make that need more acute. $\endgroup$
    – Tim B II
    Commented Feb 20, 2018 at 2:54
  • $\begingroup$ I have wondered why Tim's idea is not done now, with propane. I think probably because higher pressures are already possible but not desirable for current applications of paintball guns. It would be easy to stick a propane tank onto a paintball gun. Have a piezoelectric igniter on the trigger ignite the propane as it is released. In addition to the pressure you will have the expansion heat. I worry there might not be adequate oxygen to optimally burn the propane. So you might need 2 tanks. And for serious umph you will want to use acetylene. Please post video. Wear goggles. $\endgroup$
    – Willk
    Commented Feb 20, 2018 at 17:46
  • $\begingroup$ Small correction, Liquid hydrogen is actually very low-density (along with being a waking nightmare to contain long-term), but packs a fantastic amount of energy per-unit-mass. $\endgroup$
    – UIDAlexD
    Commented May 1, 2018 at 13:40
  • $\begingroup$ Strap a battery to your back and put a small chamber containing water behind the bullet area. Pull trigger, electrify water into Hydrogen and Oxygen, ignite with spark plug. Reload bullet, repeat. $\endgroup$ Commented Mar 3, 2019 at 3:27

You have a couple of issues to overcome here, but this is not impossible.

The first is that the air reserve will need to be replenished. Depending on the combat application this can be overcome by hand pumps or air tanks. Hand pumps are slow, but might not matter in a sniping situation. Tanks will allow for rapid fire applications, but are bulky and harder to refill quickly.

The second problem you may have is muzzle energy. The Giradoni was excellent against relatively unarmored peasants and Native Americans, but if your society has evolved to create kevlar vests with shock plates, the typical round may not have enough muzzle energy to penetrate it.

All is not lost. You can increase muzzle energy and penetrating qualities in a variety of ways. The first would be to increase the amount of pressure behind the projectile. This is done in the real world by adding more gunpowder. Make bigger and differently shaped cartridges is how this was done. For your air guns, increase the amount of air in the reserve, up the pressure in the tank and make sure your actuator and valve system. Upping the pressure in a tank will probably increase the mass of the tank, so you may have a trade off right there.

You can also increase energy by increasing the mass of the projectile. The more massive the projectile. the more air is needed to push it along. A larger bore may mean you lose something when firing. I suspect that the projectile will evolve into something more like a flechette. This will aid in your gun's ability to penetrate armor.

Your system is going to be very precisely engineered and tooled if you want big improvements on the original.

Your infantry standard is going to assume minimal training, so it will be pretty standardized. Box Magazines holing a preset number of flechettes, spring fed or gravity fed. A tank that will fire 2 or 3 magazines at a lethal muzzle velocity. A quick connect mechanism for the tank so swapping out quickly is possible. the tank connects to the butt of the rifle, maybe it even IS the butt.

Downside of air rifles set up for rapid fire is that the constantly expanding gasses is going to try to freeze the barrel, so considerations need to be made.

Sniper or long range rifles can be hand pumped or Break barrel. There are some nice varmint guns out there that reload by essentially folding the weapon in half, and that action fills the reservoir. Scale them up.

I like the idea of munitions that are less likely to cause hearing issues.

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    $\begingroup$ A tank that will fire 2 or 3 magazines without appreciable loss of muzzle velocity. - this one might be impossible, really. Unless you have reductor in place and operate your gun at pressure significantly lower than in the tank, but then your tank gets heavier. You can put it on soldier's back, but you will need air line. It gets complicated even in paintball... $\endgroup$
    – Mołot
    Commented Feb 19, 2018 at 18:54
  • $\begingroup$ @Mołot So maybe we say that a tank does 2 or three magazines at lethal velocities. Still will be heavy though. Backpack tanks are a logical thing here, but one could hope for high air capacity in a smaller tank. $\endgroup$
    – Paul TIKI
    Commented Feb 19, 2018 at 19:11
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    $\begingroup$ thank you all for your time. i have learned a lot, i also want to ask if changing the gas type would help, or to change the compounds of the tank canister to make it lighter like reinforced Aluminum (mixed metals), there are diving tanks that are very light using the same type of compounds $\endgroup$ Commented Feb 20, 2018 at 0:29
  • $\begingroup$ @CreedArcon the downside to other gasses is that you limit yourself on tank recharge. Plain old air can be refilled with a hand pump or common air compressor. Other gasses will require more exotic means. Whatever you might gain in capacity or relative mass, you lose that and more in flexibility. In warfare, logistics trumps just about everything. $\endgroup$
    – Paul TIKI
    Commented Feb 21, 2018 at 15:30
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    $\begingroup$ "I suspect the projectile will evolve into something more like a flechette." Might want to have a look at this. en.wikipedia.org/wiki/… $\endgroup$
    – UIDAlexD
    Commented May 1, 2018 at 13:43

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