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Help With Semi Auto Ideas

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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Unread postAuthor: jackssmirkingrevenge » Fri Oct 01, 2010 3:53 am

Gun Freak wrote:I think he wants bigger calliber than what a blowgun valve is good for.


For lightweight projectiles in say a 1/2" barrel, a blowgun will still do nicely, especially with some form of detent. With a properly done detent system you could even make a golf ball cannon with near burst-disk performance using just a blowgun as a valve ;)
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Unread postAuthor: Gun Freak » Fri Oct 01, 2010 5:18 pm

It will help if you glue everything after the valve into place because you won't lose air and it will make it safer than not gluing it. This is what happens when you don't glue it in... :D
[youtube]http://www.youtube.com/watch?v=3J1WfP007Mc&feature=related[/youtube]

For lightweight projectiles in say a 1/2" barrel, a blowgun will still do nicely, especially with some form of detent. With a properly done detent system you could even make a golf ball cannon with near burst-disk performance using just a blowgun as a valve

You got a point there, performance can definitely be increased by adding a detent.
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Unread postAuthor: jackssmirkingrevenge » Thu Oct 21, 2010 12:23 am

I would recommend something like this, no need for dual chambers and using a simple blowgun. The o-ring at the breech would hold the nerf dart until enough pressure built up behind it to pop it out like a champagne cork, giving you consistent power.

The major issue is the magazine, it would have to be airtight and resistant to the firing pressure of the launcher, and making a pressure vessel with flat sides is not the best of solutions. It could be built inside a section of say 2" PVC tubing though.

Another advantage of this setup is that constant pressure on the trigger should give you full auto ;)

If this is too radical you could go for the "conventional" option of combining a quick exhaust valve with a blowgun trigger likethis example which would make an airtight magazine helpful but not essential.
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Unread postAuthor: KiLlFrEnZY » Thu Oct 21, 2010 5:17 am

thanks jack...... hmmmm i always thought that this type of design would give you only one shot... without a compressor filling it would it not empty on trigger squeeze??? :? :?

clear it up for me.... to noob to get it hahahahah
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Unread postAuthor: jackssmirkingrevenge » Thu Oct 21, 2010 5:56 am

You want the detent to be set to release the projectile at a lower pressure than your chamber pressure - say 50 psi for a chamber pressure of 150 psi - and it will fire single shots with careful trigger pressure, but if you dump the tank it should fire full auto :)

This designby lozz08 works along similar lines.

The only difficulty I can see here to make it work is the choice of ammunition, a spherical projectile would be much easier to work with. Do you have your heart set of NERF darts or are you open to using other types of ammunition like airsoft BBs?

A smaller calibre would also give you more shots for a given tank volume and pressure.
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Unread postAuthor: KiLlFrEnZY » Thu Oct 21, 2010 6:00 am

well in not set on NERF darts its just that they are a readily available ammo for me.... living in Aus getting BBs is kinda bit difficult without going to ebay, and i dont to really do that if i have the choice..... but no they dont need to be Nerf darts i just thought it would be an easier option....
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Unread postAuthor: jackssmirkingrevenge » Thu Oct 21, 2010 6:16 am

KiLlFrEnZY wrote:but no they dont need to be Nerf darts i just thought it would be an easier option....


I see your point, though there are other innocuous options. Do you want this for skirmishing/friendly wargames or do you want a plinker that can do some damage? In the latter case, marbles might be worth considering ;)
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Unread postAuthor: lozz08 » Thu Oct 21, 2010 7:39 am

If you are not intending to shoot at people, then marbles would be a great choice. Using moderately sized marbles, you can have a detent-based system that pops at only 50 PSI will actually give you a decent amount of power.

And using that lower pressure will make it much easier to make a magazine because the seal won't have to be as good.
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