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pump action piston gun prototype (now with working magazine)

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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pump action piston gun prototype (now with working magazine)

Unread postAuthor: trollhameran » Tue Aug 05, 2008 3:32 pm

made my first ever piston valve yesterday :D and I wanted to make it semi, so i looked around and came across Brians falling block mechanism, so I went off and made one of them, then I had a brain wave about how to use a similar mechanism to eject cartridges. I have yet to make the mag and I still need to think of a way to only get one cartridge to fall at a time, but with it hand loaded it works, not flawlessly, but its only a prototype right.

These first pics show how the pump action works to eject the shells, the shell is loaded in the top, then the gun is fired, then when you pump the handle forward, the handle slides along the barrel and as the barrel moves back it pushes the cartridge with it, until the cartridge is half way out of "breach" at which point it falls out the bottom, then you pump the handle back and it is ready for another cartridge to be loaded. i want to make a mag for it, but i need a way to stop more than one cartridge loading at a time so that they dont all just fall out the bottom when the handle is pumped forward.
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Picture of the full gun.
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Videos

just showing the pump working
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The cartridge ejecting out the top by accident, would look cool repeated a few time
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A shot of it working properly
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It working properly again except for a slight prblem ejecting the shell
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Last edited by trollhameran on Thu Aug 07, 2008 7:11 am, edited 1 time in total.
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Unread postAuthor: SpudFarm » Tue Aug 05, 2008 3:41 pm

you have some really "interesting" designs..

me like
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Unread postAuthor: trollhameran » Tue Aug 05, 2008 4:13 pm

Lol thanks man, I have quite an "interesting" mind as well, I come up with all sorts of strange ideas and concepts,only some of which actually get put into reality.
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Unread postAuthor: jrrdw » Tue Aug 05, 2008 4:20 pm

What is the problem with the shell not ejecting in the last video clip? Any thoughts on dressing it up? Sights, scope what have you. My brother had a old Browing (i think) shot gun that ejected shells out the bottem.
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Unread postAuthor: trollhameran » Tue Aug 05, 2008 4:38 pm

The problem was I only made the pump have just enough movement to let the shells out so it got caught on the back of the wood and wouldnt fall straight away, I can fix that by making the pump move forward another 5mm or so.

When i make the next version of it, I plan to make a nice wood stock, and have all the workings, except the pump handle, hidden inside the stock to make it look cleaner, then i might put a scope on it, depending on whether I can get the mag to work or not, because if I can it will probably protrude to far out the top for the scope to be any use, otherwise ill just make it single shot and have a scope. I will also try to make cartridges seal better with the barrel to make it more air efficient.
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Unread postAuthor: jrrdw » Tue Aug 05, 2008 4:43 pm

You could all ways mount a scope on the side, I've seen a few 30-30's set up that way. Have the shells chamber against o-rings, one in front and one in the rear pushing on the shell.
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Unread postAuthor: trollhameran » Tue Aug 05, 2008 4:52 pm

Using o-rings would probably work well for sealing it.

I just had a thought for the mag. If i make the pump twice the length of the shell and only have a slot for the shells half way along it, then move the loading hole forward so that its lined up with the part of the pump with no slot, then the shells in the mag will rest on the bit with no slot, then when the pump is moved forward the shell in the gun will fall out, the slot in the pump and the loading hole will line up and the next shell will fall into place. It could work.

I think ill look up the brownings, and see what they're like.
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Unread postAuthor: bob-a-lu » Tue Aug 05, 2008 6:30 pm

i love it very innovative
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Unread postAuthor: trollhameran » Wed Aug 06, 2008 1:11 am

Thanks alot man.

Thinking about making it single shot and then for the seal at the fornt of the shells i'm going to have a ring on the end of the shell that slides into the front of the barrel so that they line up perfectly, but it wont slide in to far for it to prevent the shell ejecting properly.
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Unread postAuthor: trollhameran » Wed Aug 06, 2008 2:17 am

Sorry doubly post, Would the gun pilot well enough with a standard blowgun? I want to use one really so I can mount it in a pistol grip, so that I have an almost real trigger.
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Unread postAuthor: Darkside 6ix » Wed Aug 06, 2008 2:59 am

Yeah, ergonomics ftw. My question is have you had trouble getting the barrel to seal properly? My mind is telling me that you have a huge hole in the top of your barrel (lol). Maybe on the next version you can improve on the pump being airtight
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Unread postAuthor: trollhameran » Wed Aug 06, 2008 3:52 pm

Yeah it doesn't seal great, but I have an idea for that, the end of the barrel nearest the chamber will have rubber o ring around it which will protrude slightly out the front so the shell can push against it and seal, and then the shells will have a small ring around the front that will be the same diameter as the inside of the barrel so the front of the shell will slot into the front part of the barrel. Will do some more work on it tomorrow and se what I can come up with.
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Unread postAuthor: trollhameran » Thu Aug 07, 2008 7:10 am

I have now completely finished the prototype for this gun, it now has a working magazine and bottom ejection, all worked by the pump.

The mag is fitted on the side of the loading port so that when the pump is pushed forward, and a shell is ejected by the barrel pushing it back, the barrel blocks the next shell from rolling into the loaded position, then when the pump is pulled back again the next shell is free to roll into position ready for firing again.

Now I just need to work on the design for the actual finished gun, im planning on basing it on a browning bps deer hunter Image

Finally heres a video of the shell loading and ejection, using 3 shells.

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Unread postAuthor: jackssmirkingrevenge » Thu Aug 07, 2008 7:27 am

Very good indeed :D shame it still needs to be connected to an air line.

I love the clatter of spent cartridges, getting this to work almost brought tears to my eyes :)

Looking forward to seeing your design refined, keep it up!
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Unread postAuthor: Darkside 6ix » Thu Aug 07, 2008 7:37 am

Okay, it now dawns on me that you were using copper pipe as the shell (correct me if im wrong). Yes I definitely think that you should make a new version of this gun. Maybe you can work some of your woodcarving magic and incorporate it into the gun? :D
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