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gas system for semi auto

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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gas system for semi auto

Unread postAuthor: geardog32 » Fri Jul 17, 2009 12:23 am

i have been cruising around the spud files for a little while now and i have seen some semi auto guns but not many closed bolt type. i was just wondering if anyone has ever tried a gas tube or gas rod type of system for allowing another projectile to fall into place, just like real firearms. i have seen one golf ball gun that was a semi auto closed bolt system but it looked more like it had a sort of front block system like what you might see on auto cocker style paintball guns. i just wanted to know if this has ever been talked about? i don't know how efficient it would be for spud guns but i thought it would be a cool idea that would have a kind of novelty effect to it. it could just be built into an existing barrel just with an inner bolt with a light spring to push it forward and then a gas rod or tube to redirect gases to push it back momentarily while another projectile fell into place, after which the bolt would be closed by the spring again and be able to be fired by even an existing valve. i think this could look especially cool on some brass guns. just a 1 A.M. thought.
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Unread postAuthor: jackssmirkingrevenge » Fri Jul 17, 2009 12:29 am

The issue when trying to copy firearm mechanisms is that they work with 30-50,000 psi pressures leaving plenty of energy to work the mechanism.

That said, it certainly can be done with 3,000 psi in the FX Monsoon. If you want to apply it to spudguns, you'd have to have a relatively large chamber/air blast per shot to keep the pressure in the barrel up as well as a a large diameter piston to provide enough surface area for the low pressures to provide a decent force.
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Unread postAuthor: geardog32 » Fri Jul 17, 2009 12:53 am

this is true but i was thinking of a much lighter spring and mechanism. in both my ak and my ar15 they both have fairly hefty springs as well as heavier mechanisms and parts moving around to lock into place. i am talking about a much lighter spring and mechanism all riding on lubed up orings for minimum friction. this way its not trying to compensate for a recoil. i think that a gas rod system with a smaller area of space to fill would work better than a gas tube. i guess i was thinking more of brass guns than big spud cannons really. something sort of similar to this i know its missing a magazine hole and such but just the idea.

edit: ok i guess the fx is pretty similar but has anyone attempted this in a brass gun of there own?

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Unread postAuthor: jackssmirkingrevenge » Fri Jul 17, 2009 1:02 am

I don't think it's ever been successfully tried on a spudgun, however given the brief time interval where pressure acts on the rod I'm pretty sure that the piston diameter has to be at least larger than the barrel to be effective.

Take a look at the difference in diameter between the FX piston and its 0.22 calibre barrel, and that's at 1,500 psi minimum. Granted, it has to be strong enough to cock the fairly hefty hammer spring as well as rotate the magazine, but the mechanical advantage is there.
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Unread postAuthor: THUNDERLORD » Fri Jul 17, 2009 1:38 am

Besides the 30-50k+ psi, the solid propellant continues producing pressure even after exiting barrel. ("Underwater" firing topic).
While in spud stuff the pressure drops through barrel length (usually).
As mentioned, maybe a high volume liquid stored gas behaves similarly, but that's not practical.

Been thinking of a gas-assist for venting (exhaust) spent gasses for a rapid fire Hybrid.
A gauge would be attached to the vent hole near end of barrel to see what I'm working with before designing the gas-tube-piston assembly dimensions.

It will work regardless since even a tiny amount of pressure could be used to work an electric switch to vent the chamber after projectile passes. But then a photo-cell on end of barrel or something besides a gas tube becomes more practical.
A lever could be used in combination or a small diameter pilot valve could be tripped as well for preferable all mechanical action.

A blow-forward bolt is about the best "closed bolt" design so far.
While chamber pressure is more practical for use in loading projectile than barrel pressure also IMO.

The gas assist on firearms basically unlocks lugs holding the bolt closed after projectile passes while pressure drops to a safe level for the bolt to open.
The "Browning link" used in a Colt 1911 simply delays bolt opening as pressure has dropped.
And other short barreled designs use simple blow-back operation (Walther ppk for example)
A Mac-10/ M-11 design uses an open bolt and blow-back operation
(no gas assist, no closed bolt etc.).
The reason blow-back action works is that the pressure inside the shell casing presses outward temporararily "glueing" the shell casing in the chamber until the pressure drops where it can eject.
If the shell casing was more rigid it would work entirely differently, too thin shell casing could rupture during ejection...

My thoughts on that.
I'm more interested in the pressure (during OR before shot) closing the bolt (loading).
And gas tube (much different purpose than application for firearms) for venting spent gasses in a hybrid. 8)

EDIT: Stoner's "AR-15/ M-16" design uses gas alone (no piston) to unlock the bolt...IDK why a gas piston is mentioned...Stoner's design and Kalishnikov's (copy of the german gun) are different.
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Unread postAuthor: ramses » Fri Jul 17, 2009 9:25 am

Gas piston kits are available for AR-15s because some people think that makes them more reliable. A Gas piston is used in the AK-47.

I think that a light, low friction, gas piston would be better suited to spudguns because they require a lower volume of gas to operate. That is because in a gas only system, the gas has to expand all the way back to the bolt. This isn't a problem in real firearms because of the obscenely high pressures used.

Now you guys are making me want to attempt a shell ejecting hybrid.
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Unread postAuthor: jackssmirkingrevenge » Fri Jul 17, 2009 9:30 am

ramses wrote:Gas piston kits are available for AR-15s because some people think that makes them more reliable.


Apparently it does, look at the HK416 versus the AR.
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Unread postAuthor: inonickname » Fri Jul 17, 2009 9:49 am

THUNDERLORD wrote:A blow-forward bolt is about the best "closed bolt" design so far.
While chamber pressure is more practical for use in loading projectile than barrel pressure also IMO.

Blow forward breeches are open bolt, as the bolt closes during/before firing, rather than being closed automatically.

Have a look at my thread asking about pneumatic cylinders (and making a closed bolt semi-auto with one)
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Unread postAuthor: jackssmirkingrevenge » Sun Jul 19, 2009 3:10 am

Interesting trick to keep the pressure in the barrel up that might work as used by the AN-94 assault rifle:

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Unread postAuthor: geardog32 » Sun Jul 19, 2009 4:48 pm

very interesting the gas tube is on the bottom also, maybe to reduce the up ward part of recoil allowing higher rates of fire. it would be cool to see someone try this on a high power brass gun.
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Unread postAuthor: POLAND_SPUD » Sun Jul 19, 2009 5:27 pm

since most guns use piston valves there is need for a valve that can sequentially switch between filling/piloting... in the past I mentioned that one can use a spool valve to achieve this (either with a solenoid or manually activated)

still, a spool valve is good only for semiauto guns.. of course you can use a solenoid spool valve and use a 555timer to make it switch on/off in desired intervals but it isn't an ideal solution as it increasees complexity and wieght

However a few days ago I found this

it's a 3 way valve that switches automatically form one position to the other in 0.2 sec intervals (that's 5 RPS).. there are versions with adjustable interval as well

NOTE I couldn't find what they are called in English but I know that they are quite commonly used in pneumatic systems (which means that they are not that hard to come by)


lol sorry for going slighly off topic (as this thread is about a loading mech) but I though that this might be useful

As far as loading mechs are concerned I believe that pneumatic cylinders are ideal for most uses... I am not saying that one has to use the design I used on my semiauto but it is possibly one of the most reliable, simple and powerful design... [/url]

EDIT
ok I've found it... according to its manufacturer it's called an oscillating valve [/url]
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Unread postAuthor: Hotwired » Sun Jul 19, 2009 5:49 pm

Impulse generator or a suitably set up pneumatic timer valve.

I'm not seeing any cheap ones mind you ^^
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Unread postAuthor: POLAND_SPUD » Sun Jul 19, 2009 8:03 pm

industrial-grade pneumatic equipment is expensive... prices for a simple 3 way valve can be as high as 50-80$

fortunately, you can always find good deals on ebay or similar sites
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Unread postAuthor: SEAKING9006 » Wed Jul 22, 2009 12:20 pm

I can shed a little light on the issue on the use of a gas piston, rather than direct impingement. The problem arises from carbon fouling and dirt getting in the tube, and consrquently, to the bolt. Enough dirt and fouling on the bolt, and it jams. There's also the heat degredation that affects the bolt as well, to a lesser extent, but it's effect is less than the dirt and carbon. With a piston, the fouling, dirt, grime, sand, and water never reach the bolt. The bolt stays cleaner longer, doesn't heat up, and doesn't foul. You can open up a gas piston AR and yank the bolt right after firing it. You wouldn't dare try it with a direct impingement system, like the regular M16/M4/AR-15 systems.

It also allows you to use corrosive ammunition (like old-style laquer coated Wolf ammo) without harming the gas tube. The corrosive primers and laquer coating could easily foul a standard Bushmaster. Yet an IMI Galil can eat that junk all day long and still run like a bat out of hell.
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Unread postAuthor: THUNDERLORD » Thu Jul 23, 2009 11:15 pm

Interesting reads from replies here!!!
I've been working like crazy lately :)
so not much time to study them all fully now. :(

This part though:
SEAKING9006 wrote:...You wouldn't dare try it with a direct impingement system, like the regular M16/M4/AR-15 systems....


Reminds me of thoughts I had about some type of hydraulic "impingement" or hydraulically driven piston that's sealed off from debris completely (???) 8)

Also reminded me stories of dead soldiers found with thier rifles disassembled for cleaning, after being issued some bad "ball ammo" (with powder no longer issued)...while being over-run by mass hordes...There are "times one would dare try it"...But why need to??? :evil:
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