Dealing with ammo shortage, can you build equivalent of Cockroft-Walton generator for gas?

[hminsky]

With the shortage of ammo, I'm wondering of you can build a gas powered pneumatic rifle with as much
kinetic energy as a .223 cartridge.

You need very high pressure to replicate the gas pressure in an ignited cartridge. There's a technique used in DC-DC converters
where you make a charge pump to multiple the voltage by charging a bunch of capacitors in parallel then connecting them in series.

There's a technique they use for high voltage generators which is similar , but doesn't need any solid state switching, the Cockcroft-Walton generator

Cockcroft–Walton generator - Wikipedia

en.wikipedia.org

It charges a bunch of capacitors in parallel until they reach the breakdow voltage of air, and then suddenly they're in series.

I'm wondering if you could do the same thing with a manifold of little tanks ; you 'charge' all of them in parallel from a common
manifold from a CO2 gas cartridge, and then they have relief valves internally which connect them in series; when the pressure builds high enough, the valves
open and they are suddenly all in series, and you get a high multiple of the pressure.

If you need 55,000 psi, say, and you have a CO2 tank with 1000 psi, if you had 55 of these little micro chambers in parallel/series, could
you fire a .223 projectile with same energy as using gunpowder?

So with essentially a paintball CO2 tank, you could build a rifle that only needed projectiles, no cartridges or primers or powder. I guess question is how much volume of air is needed, so how big would the manifold array of 50 air chambers be?

It seems like they wouldn't have to be any larger than the case size of a .223 cartridge, and you 'd need 50 of them, maybe as holes drilled into
a sturdy block of aluminum?

 

[richc]

Years ago a good friend "supercharged" a paintball gun to ridiculous pressures. He's told me the stories and was punching holes through 3/4" plywood IIRC.

He's a graduate of MIT as well but older than you. But you know the mad scientist mentality that's in many MIT grads.

@Skysoldier has worked with high voltage generators IIRC. He's noodled some designs that I think are similar to what you're proposing.

Calling on @Skysoldier. Kim, what's the best way to do this?

 

[Skysoldier]

The OP's concept is comparing apples to oranges.

I don't see how you can take an array of equal pressured vessels and make them add up to a higher pressure

Build a Rail Gun!

 

[xtry51]

The OP's concept is comparing apples to oranges.

I don't see how you can take an array of equal pressured vessels and make them add up to a higher pressure

Build a Rail Gun!

This.

Pressure vessels in series are not like batteries in series. You don't get a boost.

Now what you could do is create an intensifier. You create a large biscuit to "hit" with the pressurized CO2 and press on a smaller plunger. This amplifies the force based on the area ratio.

 

[hminsky]

This.

Pressure vessels in series are not like batteries in series. You don't get a boost.

Now what you could do is create an intensifier. You create a large biscuit to "hit" with the pressurized CO2 and press on a smaller plunger. This amplifies the force based on the area ratio.

Yeah I guess pressure vessels aren’t additive in the same way that voltages through capacitors are. If you connect one 1000psi cylinder to another, they just result in a 1000psi pressure source with twice the volume/flow capacity. But there is a concept called a Clark Pump used in reverse osmosis water maker desalinators on boats that uses a simple 12V low pressure pump to generate something like 80psi of pressure at a nominal flow rate of say 10gal/min and the clark pump converts that to something like 800psi at 1gal/min or a little less since there’s excess low pressure water spilled out to run the pump.

Like you're describing, in hydraulics a relatively low pressure system can “multiply” the pressure by applying it to a 2 stage piston which has a large surface area/volume on the low pressure side and a small surface area/volume on the high pressure side; push 100 psi of oil into a 10 sq. in. piston diameter and it’ll push a 1 sq. in. piston with 10 times the pressure. I think this dual stage piston could produce this kind of amplification; charge up a large-ish reservoir of the 1000psi CO2 then release it onto a large diameter piston which is pushing a small diameter piston. The diameter ratio would have to be 55:1, but the small one could be pretty small if you don’t need a ton of the high pressure charge. I’m assuming that a typical bullet only has 55kpsi for a fraction of it’s travel down the gun bore, so you hopefully wouldn’t need a ton of volume. Not really as elegant as the charge pump… perhaps there’s another way to multiply pressure using Bernoulli or other compressed gas principles. Or maybe just a lithium battery powered high pressure pump using that hydraulic amplification? Maybe have several high pressure chamber cylinders so one is recharging while the other fires?

 

[Uzi2]

Any .45cal slug moving at 800 fps hitting you in the head is a mortal wound. That velocity is easily attainable with simple pneumatics.

 

[xtry51]

Yeah I guess pressure vessels aren’t additive in the same way that voltages through capacitors are. If you connect one 1000psi cylinder to another, they just result in a 1000psi pressure source with twice the volume/flow capacity. But there is a concept called a Clark Pump used in reverse osmosis water maker desalinators on boats that uses a simple 12V low pressure pump to generate something like 80psi of pressure at a nominal flow rate of say 10gal/min and the clark pump converts that to something like 800psi at 1gal/min or a little less since there’s excess low pressure water spilled out to run the pump.

Like you're describing, in hydraulics a relatively low pressure system can “multiply” the pressure by applying it to a 2 stage piston which has a large surface area/volume on the low pressure side and a small surface area/volume on the high pressure side; push 100 psi of oil into a 10 sq. in. piston diameter and it’ll push a 1 sq. in. piston with 10 times the pressure. I think this dual stage piston could produce this kind of amplification; charge up a large-ish reservoir of the 1000psi CO2 then release it onto a large diameter piston which is pushing a small diameter piston. The diameter ratio would have to be 55:1, but the small one could be pretty small if you don’t need a ton of the high pressure charge. I’m assuming that a typical bullet only has 55kpsi for a fraction of it’s travel down the gun bore, so you hopefully wouldn’t need a ton of volume. Not really as elegant as the charge pump… perhaps there’s another way to multiply pressure using Bernoulli or other compressed gas principles. Or maybe just a lithium battery powered high pressure pump using that hydraulic amplification? Maybe have several high pressure chamber cylinders so one is recharging while the other fires?

It may be possible to use lower PSI in larger volumes to run a mini compressor to build a higher charge slowly. The losses would be high though.

A rail gun is definitely a better pursuit here.

 

[Broc]

Paging @Rusty Shackleford he always has great ideas about stuff like this.

 

[Boris]

Yeah I guess pressure vessels aren’t additive in the same way that voltages through capacitors are. If you connect one 1000psi cylinder to another, they just result in a 1000psi pressure source with twice the volume/flow capacity. But there is a concept called a Clark Pump used in reverse osmosis water maker desalinators on boats that uses a simple 12V low pressure pump to generate something like 80psi of pressure at a nominal flow rate of say 10gal/min and the clark pump converts that to something like 800psi at 1gal/min or a little less since there’s excess low pressure water spilled out to run the pump.

Like you're describing, in hydraulics a relatively low pressure system can “multiply” the pressure by applying it to a 2 stage piston which has a large surface area/volume on the low pressure side and a small surface area/volume on the high pressure side; push 100 psi of oil into a 10 sq. in. piston diameter and it’ll push a 1 sq. in. piston with 10 times the pressure. I think this dual stage piston could produce this kind of amplification; charge up a large-ish reservoir of the 1000psi CO2 then release it onto a large diameter piston which is pushing a small diameter piston. The diameter ratio would have to be 55:1, but the small one could be pretty small if you don’t need a ton of the high pressure charge. I’m assuming that a typical bullet only has 55kpsi for a fraction of it’s travel down the gun bore, so you hopefully wouldn’t need a ton of volume. Not really as elegant as the charge pump… perhaps there’s another way to multiply pressure using Bernoulli or other compressed gas principles. Or maybe just a lithium battery powered high pressure pump using that hydraulic amplification? Maybe have several high pressure chamber cylinders so one is recharging while the other fires?

they are called pressure boosters and are used in hydraulics as well as in pneumatics. So yes, you are not wrong.

8mm Mauser bullet has energy of about 4kJ. MG42 discharges about 25 of them per second. So that's 100kJ/sec or 100kW or 134 Hp. So yes, you can theoretically use a few cylinders of your minivan to run powderless mg .... which would be absolutely legal per ATF.