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cartridge fed pneumatic prototype

Built a pneumatic cannon? Then post it here! This section is for completed, finished cannons that you have built. Please include pictures and information.
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Unread postAuthor: jackssmirkingrevenge » Fri Apr 06, 2007 9:36 am

Thanks for the positive feedback guys.

Hawkeye wrote:Some more thoughts on this concept... Perhaps the bolt should be housed in a cylinder that allows it to be airtight or reasonably so as it blows back for a further distance. It looks like the air shoots the projectile and the casing back but then right away there is an open vent at the magazine slot for air to exit and bleed off power.


When you compare the weight (and therefore the rate of acceleration) of the cartridge (which is also being held by the bolt spring to the pellet, the latter would actually have left the barrel by the time the cartridge is out of the breech and air can bleed out, so this isn't an issue.

Weaxle, I can't really give you a "how to" because I made this with materials I had to hand - however if you look at the concept, it's fairly simple to understand and anyone reasonably competent could adapt the idea to the resources he had to hand.
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Unread postAuthor: Hawkeye » Fri Apr 06, 2007 11:17 am

Maybe so, but looking at your diagram and actual prototype it appears that there is about less than half an inch of rearward travel before those holes in the cartridge are exposed.
You don't think a little extra room would help in the off the chance things aren't working exactly as the technical aspects suggest they should?
Why is the power so low? Maybe you could jam the bolt and see just how much power it has without moving the cartridge and bolt.
Of course I'll have to go ahead and make one that contains the air "explosion" a bit longer to see if it makes a difference. The higher pressure and flow will skew that a bit anyway. I just want to see one rattle off a series of five shots or so and spit those casings out the side. :)
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Unread postAuthor: thrasmussen » Fri Apr 06, 2007 8:46 pm

Could work better, you just need to adjust it.
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Unread postAuthor: VH_man » Fri Apr 06, 2007 10:00 pm

If you havent fixed the low power problem already, try covering the WHOLE shell in holes...... it may sound like a dumb idea but it seems like the second the shell travels backwards airflow stops travelling through the barrel..... just a thought...... and by the way if its OK with you im making a shell fed nerf gun on your concept....... (well, i SAY its nerf, but really im launching blowgun darts)
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Unread postAuthor: jackssmirkingrevenge » Sat Apr 07, 2007 4:17 am

Some valid points there Hawkeye, to be honest I was so elated at actually getting it to work that I rested on my laurels prematurely and failed to tweak the system further. I would tend to agree that yes, a longer breech and/or a stiffer spring would make the launcher more powerful. Also, moving the extractor back would hold the bolt back more and give the next cartridge more time to move into place, probably eliminating the need for a bolt stop.

VH_man, I don't think that would help much because the air is only blocked until the cart clears the transfer port, after that it's back to maximum flow. Feel free to use and develop the design, I don't claim any copyright over it.
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Unread postAuthor: zeigs spud » Sat Apr 07, 2007 8:45 pm

experament-u2 wrote:i think u are my new hero :lol:
that is awsome i woudl love to see a pistol desgined around that


yes, many have dreamed of makin it but you did it great job!
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Unread postAuthor: Boomer_ » Sun Apr 08, 2007 4:25 pm

Could you make a larger bore model of this? Also, doesn't the weight/mass/fit of the projectile play a big part in this system? I would think that the projectile would have to fit well enough to throw the casing backwards as well as the projectile forwards. Correct me if I'm wrong, I am extremely interested as I have been planning something almost exactly like this design only a bit bigger. Thanks.
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Unread postAuthor: Hawkeye » Sun Apr 08, 2007 7:44 pm

Obviously the better the fit of everything, the better the system will work. I have scaled it up for marbles and am hoping that making a heavier bolt that travels farther back and is cushioned(and returned) by a long soft spring will give it more time to cycle.
The marble will exit the barrel and the bolt will no longer actually still be propelled back by air, but it should have momentum in its favor.
The carts will be sections of half inch copper with an end cap and a section of coupler on the front so they travel level in the blowback cylinder.
Unfortunately I can't seem to figure out a way to totally eliminate dead space but it is fairly minimal.
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Unread postAuthor: Flying_Salt » Sun Apr 08, 2007 7:53 pm

And Killagorilla claimed to be God...
That's really awesome, but the awesomest thing is that I use smiley face targets too! (But I use spraypaint on a carboard box)
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Unread postAuthor: DasGestapo » Sun Apr 08, 2007 8:04 pm

that is sick!!
i was actually considering something similar
recently i have been working on a kit to convert a paintball marker to fire 8mm airsoft bbs
oh well
i love the cartridge ejection
nice work!!
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Unread postAuthor: jackssmirkingrevenge » Mon Apr 09, 2007 4:06 am

Hawkeye wrote:Obviously the better the fit of everything, the better the system will work. I have scaled it up for marbles and am hoping that making a heavier bolt that travels farther back and is cushioned(and returned) by a long soft spring will give it more time to cycle.


That's the tricky part for semi-auto operation - giving the next cartridge enough time to fall into place before the bolt returns. You could help it with a spring loaded magazine, but you can't apply too much pressure as this would cause friction that could potentially prevent the bolt from moving sufficiently.

With my combustion cartridge prototype, the solution I used was to replace the bolt spring with a pneumatic piston. This returned slowly due to the friction with the seal. It's a more complex system but had the advantage of being able to adjust the stiffness by altering the chamber pressure.

Image

Image

Another solution would be to use the returning bolt to pick up the cartridge in the manner of a real firearm.

[youtube]http://www.youtube.com/watch?v=G0VjdI_S_HM[/youtube]
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Unread postAuthor: joannaardway » Mon Apr 09, 2007 12:33 pm

My brother would kill me if he finds out I've told you this, but he stole parts of the idea from me - which I got from this in the first place - so he can get stuffed.

He's got an idea he calls the "Jackhammer" semi-auto system - because it works on a similiar operation principle to a jackhammer, apparently.

The basic component is a double-acting pneumatic cylinder, where the positive side is connected to a small reservoir of compressed air at about 30 psi or so (the exact pressure you need will vary), and the negative acting side is linked directly into the pneumatic's chamber (at a higher pressure).

The cylinder is intially in the negative postion (because of the higher force), until the chamber depressurizes immediately after firing, in which case the cylinder switches ends, allowing a reloader to be operated. Repressurizing the chamber would return the cylinder automatically.

The exact return speed can be controlled by how fast the chamber is filled, and the speed at which the cylinder pushes the bolt back is determined by the pressure in the small reservoir.

The wonderful thing about the design is that it's reliable, and no energy is lost from the projectile, because the cylinder operates well after the projectile has left the barrel.
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Unread postAuthor: jackssmirkingrevenge » Mon Apr 09, 2007 12:42 pm

That makes sense, but it sounds very wasteful of air.
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Unread postAuthor: Hawkeye » Mon Apr 09, 2007 3:32 pm

I'm pretty sure I've figured out a way to have the bolt travel back far enough with the spent cartridge linked to it to allow enough time for a fresh cart to drop down and be pushed into the breech by the returning bolt.
During that rearward travel the spent cartridge will be kicked out an ejection port of course .
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Unread postAuthor: veginator » Tue Apr 10, 2007 4:08 pm

Nice cannon, oh and by the way i'm new here
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