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Piston Gun That Shoots Multiple Times

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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Piston Gun That Shoots Multiple Times

Unread postAuthor: cowscankill » Wed Dec 23, 2015 12:10 am

This has probably been done before, but I never actually looked for this design/idea and it just randomly hit me one night. It just makes sooo much sense to add a larger primary chamber to the inlet of a piston gun, and minimize the size of the secondary. Slap on any kind of valve and wammo, you have a multishot gun.

This was the first gun I designed in it's entirety before just slapping stuff together so I was able to make it a bit sleeker and calculate random stuff like volume and pressure:
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Because there is no regulator the pressure drops off pretty quickly:
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Overall I'm happy with how it came out, but I haven't actually shot anything yet. Here's a nice blurry picture:
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Considering this is pretty much the same material as any other gun I've made, I'll probably try testing it up to 120 PSI, but I usually just chill at 100 for having some fun. I'll have more videos and stuff later to actually explain the parts and get some destruction footage. For now I leave you with this preview:
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Re: Piston Gun That Shoots Multiple Times

Unread postAuthor: jackssmirkingrevenge » Wed Dec 23, 2015 6:54 pm

Nicely done, are the pressure/shot values measured or theoretical?
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Re: Piston Gun That Shoots Multiple Times

Unread postAuthor: cowscankill » Thu Dec 24, 2015 12:50 am

jackssmirkingrevenge wrote:Nicely done, are the pressure/shot values measured or theoretical?


Theoretical, could even be higher than what is on the video because I think the chamber I ended up using is bigger.

I don't wanna put a small gauge on my gun until I have something worthy of it :P And my bike pump has a bent needle and stuff so it's hard to even get a multiple of ten easily on that gauge.
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Re: Piston Gun That Shoots Multiple Times

Unread postAuthor: bravootome » Thu Dec 24, 2015 10:56 am

i think you would love a 40 bar hammervalve, 5,5 or 6 mm. ( for out door use)
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Re: Piston Gun That Shoots Multiple Times

Unread postAuthor: Gun Freak » Thu Dec 24, 2015 1:51 pm

Looks like a very fun little plinker! I personally would have used a larger diameter pipe for your reservoir so that the pressure wouldn't drop off so fast. Have you tried cracking the valve ever so slightly so that it automatically fills up the chamber without majorly affecting piloting?
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Re: Piston Gun That Shoots Multiple Times

Unread postAuthor: cowscankill » Thu Dec 24, 2015 8:57 pm

It's been storming for like 3 days straight, over 70F outside. Jeez, this doesn't feel like winter break at all.
Since I haven't really been able to shoot or paint anything, I just made a bipod cause I've always wanted one. I'm fairly happy with how it turned out, but it still needs some rubber feet and stuff.
Image
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Still looking for things to add to the gun until I can actually start shooting. Perhaps I'll add sights onto my gun for the first time ever. Only problem is that the barrel can twist/wobble, but maybe I'll come up with something.

Gun Freak wrote: I personally would have used a larger diameter pipe for your reservoir so that the pressure wouldn't drop off so fast.


I found if I increased the pipe diameter from 1" to 1-1/4", I would get about one extra shot off before dropping from 100 PSI to ~50 PSI (5 shots with 1", 6 shots with 1-1/4"). I like trying to design guns with a bit of style and sleekness so that one extra shot in exchange for a bulkier body wasn't quite worth it to me.

Gun Freak wrote: Have you tried cracking the valve ever so slightly so that it automatically fills up the chamber without majorly affecting piloting?


Huh, I actually never considered doing that. I'll try it out a bit and see what happens.

EDIT: Well, it looks like I just accidentally made my first semi auto. Huh.
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Re: Piston Gun That Shoots Multiple Times

Unread postAuthor: mark.f » Sun Dec 27, 2015 9:08 am

Of course, if I don't recommend it, poland_spud will come along and do it, so...

You can accomplish the same semi-automatic firing by replacing the cracked ball valve with a three-way valve for filling and piloting, which will fill faster (depending on the valve you buy) and reduce losses when piloting. :wink:

Good job though! Using lower pressures and lightweight projectiles, you can definitely get a boatload of shots from that reservoir. Have you considered using a regulator to fill the "firing chamber" to a lower pressure than the reservoir? Instead of starting at say 120 PSI and reducing power each shot, why not fill the reservoir to 120 and regulate down to, say, 15-30 PSI for nerf darts?
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Re: Piston Gun That Shoots Multiple Times

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Re: Piston Gun That Shoots Multiple Times

Unread postAuthor: cowscankill » Wed Dec 30, 2015 12:20 am

mark.f wrote:Have you considered using a regulator to fill the "firing chamber" to a lower pressure than the reservoir? Instead of starting at say 120 PSI and reducing power each shot, why not fill the reservoir to 120 and regulate down to, say, 15-30 PSI for nerf darts?


I have considered that actually, and I might on my next project.
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Re: Piston Gun That Shoots Multiple Times

Unread postAuthor: Hammond Grey » Tue Apr 05, 2016 9:09 am

I'm new to spudfiles and airguns generally. I would appreaciate it if you could give us a tutorial, especially on the piston valve and breech. Thanks in advance.
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