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Automatic Fire

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Unread postAuthor: judgment_arms » Mon Jun 04, 2007 1:24 pm

Hay all!
I’m attempting to make a .75cal pneumatic light/sub machine gun but I’ve run out of ground, so to speak…
The primary ammunition I hope to use is wadded paintballs (going back to my old paintball rifle idea.) in “cases” about 2-3 inches long with a “rim”, much like the old black powder cartridges and shotgun shells for extraction.

Now then, to the part that has stumped me: cycling.
Half the point of this project is to see if it’s possible for a low-pressure pneumatic MG to use the same pressure used to fire the round to cycle the action and still have a usable muzzle velocity, much like a firearm.

I know, for a fact, that blow-back works, but won’t yield much power at all, so I’ll need some form of delay mechanism to get a usable velocity (250+fps).
Gas-delayed blow-back would be simple to make, but would a chamber pressure of 80-100psi be enough to make it work?
Or perhaps maybe a friction delayed mechanism, i.e. the front of the chamber being slightly smaller diameter than the rest giving the same affect as and un-glued end-cap, it’ll hold for a second, but then break away.

I’ve also gave some thought to short-recoil operation, much like the Browning M1919 and M2 machine guns. But I’m not sure if that’s even plausible seeing how those shoot .30-06 and .50bmg not paintballs…

Any help will be appreciated, thanks in advance.
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Unread postAuthor: joannaardway » Mon Jun 04, 2007 2:17 pm

Can I suggest the Jackhammer reloader method my brother came up with?

You need a pneumatic cylinder (linked to your bolt), with one port connected to a suitably low pressure vessel.
The other port of that is connected to the chamber.
When the chamber pressurized, the cylinder is one way. Immediately after firing, the pressure will fall below that of the other port, so the cylinder moves the other way.
Repressurizing moves the cylinder back.

It should do the trick for you, and it has no "real" air consumption.

Does that make sense?
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Unread postAuthor: judgment_arms » Mon Jun 04, 2007 2:25 pm

Makes perfect sense, but I didn’t want to use an external force to cycle the action, such as a pneumatic cylinder.
Thanks anyways.
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Unread postAuthor: Suppressive Fire » Mon Jun 04, 2007 6:10 pm

I have a diagram on a method that I'm attempting to pioneer. Gas operated reload, this method draws air from the barrel after the projectile clears a gas draw port which is about 3/4 of the way down the barrel. There is also another method that I have a diagram of but I can't seem to upload the diagrams. I can however try to email them to you if you want. Just email or pm me if you want them and I'll do my best.
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Unread postAuthor: us sniper » Mon Jun 04, 2007 6:16 pm

Why don't you use a motor that pulls the bolt back. Then thepaintballs fall in, the motor shuts off and a spring forces the bolt forward. The motor would only be enough to counter the spring when it is turned on. You would control the motor by having an on and off switch hooked up to your trigger. Then your gun would be a semi-automatic.
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Unread postAuthor: judgment_arms » Mon Jun 04, 2007 7:19 pm

Us sniper, I’ve already said I do not wish to use an external power source. But thanks anyway.
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Unread postAuthor: turbohacker » Mon Jun 04, 2007 7:33 pm

mabee in place of the motor a pnumatic ram that is acuated by the trigger or the shot itself?
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Unread postAuthor: judgment_arms » Mon Jun 04, 2007 9:41 pm

…I guess I did say “any help will be appreciated”…
Okay I’ll say it again,
I do not want to use any outside force to cycle the action, no motors, no gas rams, nothing, just the same power sources as would be on a firearm, and I’m not talking Bushmaster or GE Mini gun, more like BAR, MG42, M1919, Thompson Sub-Machine gun, or the M1.
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Unread postAuthor: jackssmirkingrevenge » Tue Jun 05, 2007 3:32 am

how about the blow-forward valve as clide used on his GB semi?
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Unread postAuthor: judgment_arms » Tue Jun 05, 2007 8:39 am

It has bean considered, but I decided not to use it for two reasons:
One, I don’t want all the valves and stuff behind the receiver; I’m going for the M1919A6 look, except top feed side eject like the Chatellerault. Basically, once completed, I want it to look like something out of WWII, something that won’t look out of place sitting between a halftrack and a Sherman…

And two, the “round” I’m using will be used on future guns, and is all but built. I got the idea for it from your semi-auto, jack. It’s a piece of ¾” pipe about three inches long, sealed at the back with a ring of holes around the middle, much like an enlarged, plastic, version of the cartridges used by your semi-auto.
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Unread postAuthor: jackssmirkingrevenge » Tue Jun 05, 2007 8:56 am

ahhh... I always wanted to scale it up to 3/4". Are you sure direct blowback with a good high-flow valve and a stiff spring won't work well? given the cart's larger mass and the fact that its being held by the spring, the round should be out of the barrel long before the cart mouth leaves the breech, I don't see why 250 fps shouldn't be feasible.
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Unread postAuthor: ShowNoMercy » Tue Jun 05, 2007 9:48 am

I know that you said that you dont like clides slider design, but I made one out of metal and it looks like a piece of metal. You could do so much with it to make it more real looking. Dont be put off by the looks of the slider, it was a prototype and not designed to look military. And why bother with casings? I know that it will look realistic but also add to the complexity of the gun.
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Unread postAuthor: judgment_arms » Tue Jun 05, 2007 10:42 am

Why bother with cases? Simply put, because I can.
I must do things backwards; I designed the cartridge, then the gun. Were as you seem to design the gun then the cartridge, or lack there of, to suit…

Back to Jack,
Yeah if I had I high performance valve it might, but I’m look at a 1” modded sprinkler valve, or even a slide valve, due to size restraints.
Perhaps I should go with a small piston valve. Would a half-way decent half to three quarter inch piston valve out perform a modded one inch sprinkler? More importantly, which would close faster?
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Unread postAuthor: iknowmy3tables » Tue Jun 05, 2007 11:32 am

how did i miss this thread, first this will never be submachine gun sized, and now I'd recommend something similar the jack hammer however spring return and locking bolt because I have been worried about the delay on that system, second direct blow back maybe but I recently thought of a variation of that where the spring return is replaced with pneumatic cylinder that is attached to the chamber so every time the chamber fills the bolt closes this is better then a spring since the force is not seen a exponential growth (the force increases more and more as you pull back) in stead use a pneumatic cam return with a roller delay, allowing it to open at the peak of force then glide easily into the retun with the remaining force
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Unread postAuthor: jackssmirkingrevenge » Tue Jun 05, 2007 11:35 am

ShowNoMercy wrote:And why bother with casings? I know that it will look realistic but also add to the complexity of the gun.


Because they look cool, that's reason enough for me :D

I'm sure a 1" modded sprinkler valve would do the trick, though I can't tell you how fast it would close.

It depends how many operations you'd like to include per shot - to ensure almost immediat closing, you could have the chamber refilled through the pilot area of the sprinkler, which means you open a valve to fill the chamber, then close it and open another valve to pilot the sprinkler.

I'm sure there are three way valves out there that would enaple you to carry out this operation with the single push of a button.
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