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Some thoughts on automatics

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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Re: Some thoughts on automatics

Unread postAuthor: judgment_arms » Mon Apr 28, 2008 9:27 pm

Ragnarok wrote:Sounds like a pretty decent write-up.
I've never been too keen on the conventional methods of auto-loading myself.
Most, other than the obvious blow-forward bolt, are all designs developed for firearms, and although some can be operated successfully on spudgun pressures, my choice would be to use a different loading mechanism.
None of the conventional designs will get away without affecting a launcher's power, and when scarce little is available to begin with anyway, losing some to a loader isn't very tempting.

Seeing as how I only need 300fps from a single paintball, power ain’t much of a concern. ;)
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Unread postAuthor: POLAND_SPUD » Mon Apr 28, 2008 9:47 pm

judge thanks for this thread
since JSR wrote some time ago that blowback doesn't work well I never bothered to try it but now I see that I have to experiment with it

@ ragnarok
I developed one a while back, which got dubbed the Jackhammer design. It involved a pneumatic cylinder directly connected to the chamber in such a way that the loader was held shut when the system was under pressure.
When the pressure fell (i.e. after firing), a lower pressure fed to the other side of the cylinder would push it open again. Re-pressurizing the chamber would close the bolt again.
I had a similar idea long time ago but I thought about using a single acting air cylinder and a slide valve... a slide valve would stop the air form getting into the chamber upon piloting the gun and I assume that it would give enough time for the cylinder to reset

so far I've never tried this design becasue it's rather difficult to find an air cylinder with as small diameter as possible and pressure rating higher than 10 bar
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Unread postAuthor: jackssmirkingrevenge » Tue Apr 29, 2008 1:44 am

Also, on this subject was an idea put forward by my dad of having a large disc with holes in it that acted as both valve and breach.
As the disk spun it lined up with a tube the pushed a paintball into a hole in the disk, as it continued to rotate it lined up with the chamber and barrel, the air would dump from the chamber, though the disk, and push the paintball out the barrel.
Obvious problems with this design include the need to a rotating disk and that, if not spinning vary fast, the valve would open painfully slow.


Conceptually similar to this?

Image

I believe it was actually tested to some extent, not by me though.

As mentioned here, I think a rotating axis perpendicular to the barrel us a better idea - basically, if the hole through your rotating disk is very close to the diameter of the projectile, then it will effectively seal the tube until it's in line with the barrel. This means that at the moment of firing (ie when the projectile is released) you already have maximum flow, meaning it's practically like having a burst disk ;)

since JSR wrote some time ago that blowback doesn't work well I never bothered to try it but now I see that I have to experiment with it


It doesn't work well at low pressures, but for example the Caselman has a direct blowback reload mechanism, which it can afford because of the 3,000 or so psi it's designed for.

Also note that my cartridge fed protype also has a blowback mechanism, though in conjunction with a piston valve.

One way of making it work is possibly to increase the area of the bolt surface on which the air acts upon, I had thought of something like the following but never built it:

Image
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Unread postAuthor: Hydra » Tue Apr 29, 2008 3:21 am

Instead of a cut-out, could you cut a long, deep knotch in the middle of the rotor that goes all the way through? And you have the air input from directly behind the rotor. Its kinda like a heavily modified, motor operated ball valve. A picture might explain better.
This could make a sort of fully automatic shotgun if you do it on large scale, where there could be like 15 projectiles sitting in the knotch.

Everytime the knotch lines up with the air input, the ammo in the knotch will go flying out. When the knotch is perpendicular to the air (closed), the ammo will be given a chance to fall into the long knotch, then when the knotch connects to the air, they go flying out again and it all repeats until you run out of ammo.
Image
Red=Rotor
Dark Red=Knotch
Light Blue=Air
Dark Blue=Ammo
Dark Red circles=Where the motor connects to the rotor. xD Rhymes.
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Re: Some thoughts on automatics

Unread postAuthor: Ragnarok » Tue Apr 29, 2008 5:14 am

judgment_arms wrote:Seeing as how I only need 300fps from a single paintball, power ain’t much of a concern.

Fair dos, but being more efficent with your gas use is always an advantage.
Assuming that for a PB automatic, you're drawing from a limited gas volume (CO2 or HPA tank), why use more of that than you need to?
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Unread postAuthor: judgment_arms » Tue Apr 29, 2008 9:24 am

Ragnarok wrote:Fair dos, but being more efficent with your gas use is always an advantage.
Assuming that for a PB automatic, you're drawing from a limited gas volume (CO2 or HPA tank), why use more of that than you need to?

Which is why most all of my designs work on low pressure air, usually under 120psi, so that, one, I can run it of the air compressor, and two, a given volume of high pressure gas will power it longer.

But I do see your point.

Still, I prefer to use familiar operating mechanisms, I’m a firearms guy, so firearm operating mechanisms are very familiar…





jackssmirkingrevenge wrote:Conceptually similar to this?

Image


Yes, but rather then only one hole, he had ~10, the disk was to be the size of a dinner plate, and ran vertical rather than horizontal.
Although, with that many holes the chance for an appreciable amount of pressure to build up would be small, unless spun slowly…

Brings to mind the idea that spawned this one, a Lewis gun style magazine for feeding paintballs on a very early design for a paintball HMG…
:shock:
Great Scott!! I just solved the “looks” problem with one of my machine gun designs, and the feed problem!





POLAND_SPUD wrote:judge thanks for this thread
since JSR wrote some time ago that blowback doesn't work well I never bothered to try it but now I see that I have to experiment with it

If your using a low pressure system you’ll want a delay mechanism, perhaps a toggle delay like on the Luger P.08; it would be interesting if nothing else. :)
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Unread postAuthor: Ragnarok » Tue Apr 29, 2008 5:03 pm

Hmm, I've been given an idea.
I've wanted to build a rapid fire launcher of some sort for sometime, most likely either pump or semi.

However, the problem posed is extra dead volume, loss of pressure to work loaders, that kind of thing. The jackhammer loader design went part way to solving that, but it's only just occured to me. What about a different jackhammer?

...The Pancor Jackhammer shotgun.
I would be perfectly capable of creating a loader that worked like that, although the revolving magazine would probably be fixed to the launcher, only about 6 rounds, and unlikely to be full auto.

But it would still be cool, and it gets around certain problems like dead space, and magazine feeds at odd angles. Ideas will need to be ironed out, but I might well have an idea for my next project there.
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Unread postAuthor: jackssmirkingrevenge » Wed Apr 30, 2008 12:18 am

If your using a low pressure system you’ll want a delay mechanism, perhaps a toggle delay like on the Luger P.08; it would be interesting if nothing else.


I doubt that would be worthwhile, a delayed breech might be necessary on a 9x19mm pistol but on anything less, direct blowback is more than enough. If nothing else there won't be a sufficient pressure impulse to allow for any delay, you want the bolt to start moving as soon as the projectile does. otherwise after the projectile leaves the barrel the pressure drop won't allow for any spare energy to move it.
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Unread postAuthor: JDP12 » Wed Apr 30, 2008 7:22 am

darnit JSR... beat me to it, i was going to say that a delay might not even be possible.... grr..
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Unread postAuthor: judgment_arms » Wed Apr 30, 2008 8:26 am

The toggle delay would be fine, if done right, it can be set up to where there’s hardly a delay at all.
It works by holding the bolt shut until the pressure drops below a certain point, dictated by the springs in the toggle, then allowing it to open.
So, if one used light enough springs then the toggle could be timed to only hold it shut for a couple of milliseconds, just long enough for the projectile to develop sufficient velocity, and then open.

On the other hand, such a mechanism would be immensely complicated and hard to tune, probably not the best suggestion.

Humm… it occurs to me that when I recommended toggle delay, I was assuming he was going to build a large cannon, and on a cannon of sufficient size a delay mechanism would be practical, but if the bore is 1 inch or less and/or the chamber not huge, then I could see how a delayed mechanism wouldn’t work.

On the other hand, if the cannon is too small for delayed blow-back then it’s not going to have any power at all with pure blow-back…
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Last edited by judgment_arms on Wed Apr 30, 2008 9:39 am, edited 1 time in total.
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Unread postAuthor: THUNDERLORD » Wed Apr 30, 2008 8:58 am

Getting back to your original gas assist, whether it's toggle action or other locking bolt method (revolving bolt lugs etc.) Why not still attempt to use gas assisted opening? It would vent some of the propelling gas but only inches form the muzzle.

Also Judgement_Arms, I think your bolt ideas a few replies back seem valid.
It's interesting that a "hang fire" in a firearm is when the round does not fire milliseconds from the trigger pull.

Its kind of funny that with a lot of spud type designs most people are happy to get it to fire within seconds.
With some designs the first shot(s) is delayed before continuos fire is acheived.
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Unread postAuthor: iknowmy3tables » Wed Apr 30, 2008 3:24 pm

gas operated more reliable than blowback? in low presures? it doesn't make sense, sure you have the results but it must be explained. from what I see blowback is suppose to have more force for cycling because it utilizes gas from a point that is farther back and has greater pressure, as we know direct blow back is not used on lager calibers because of the force is too strong, I think the problem with the cartridges was the stroke length, from what I remember about guns longer strokes do prove less reliable. and clearly the stroke is way more than than the 3 inches the gas operation provides.
and the gas operation test neglects to opening of the breech which would cause sudden pressure vent

you might want to scratch that judgment arms, blowback should work fine with shorter stroke lengths and larger diameter breeches
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Unread postAuthor: POLAND_SPUD » Wed Apr 30, 2008 4:31 pm

I think that high mass of the bolt would be enough to make sure that it opens after the projectile leaves the barrel and that I would still have enough momentum to allow to load new ammo... obviuosly the bolt needs to be heavier than the projectile it fires but the only question is how heavy ?

after reading some of JSR posts on blowback I think that it can work... first of all he used low pressures and the gun he used were small bore as a result there was not enough force acting on the blowback mechanism to overcome the friction from o-ring/s and consequently his gun couldnt operate properly
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Unread postAuthor: THUNDERLORD » Thu May 01, 2008 12:57 am

There is a factor that is much different from shell casings for firearms to get the shell to eject.

That is that if your shell casing holds the same pressure as the barrel it doesn't even need a chamber.

All it needs is a small area to have a seal between the casing and the barrel.

That area could be as small as say 1/4" That's all the movement the bolt needs to travel.

Since the casing will not flex and glue itself in place it needs no shell extractor (the little clip on the bolt of a firearm that clips on the thin casing to pull it out).

With a heavy shell it really doesn't need much of a ejector either.
Because the thicker shell needing no chamber only has to move that fraction of what a thin casing would need to travel(it's full length).

It's really a lot more simple than a firearm mechanism, the shell could drop in from the top the bolt pushes it only slightly forward it fires the gas assist unlocks or assists the rearward pressure on the spring
and it could even gravity eject out a slot in the bottom or it could blowback the fraction of it's length smack the ejector and eject that way.
Either way by having a shell that can hold the same pressure as the barrel not nearly as much pressure is needed as a firearm casing.

Perhaps that's why some others misunderstood my reply. :roll:
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Unread postAuthor: judgment_arms » Thu May 01, 2008 6:40 am

THUNDERLORD, you’re going to run into a problem, when the valve opens the gas will hit the projectile, with no way to lock the bolt to the barrel the minute any pressure hits the cartridge it’ll pop the bolt right off, if not then, once the projectile enters the barrel, then it’ll commence cycling, producing very little to no performance.

This is what Jack meant be using a longer traveling bolt, the pressure circuit will stay closed longer.


POLAND_SPUD, you seem to misunderstand me, I’m not saying it won’t work, I’ve proven that it will indeed work, what I’m saying is that you will get no power from pure blowback in a LP cannon.

Iknowmy3tables, shorter stroke lengths and larger dia. breaches will only worsen performance because it will cause the bolt to open sooner.
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