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pcp airgun from fire extinguisher

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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pcp airgun from fire extinguisher

Unread postAuthor: human » Fri Jan 14, 2011 11:56 am

Today i finished my airgun! thought i'd share it with you guys.

Tank is filled up to 14 bars using a bicycle pump, then i can shoot 20 times or so..

if the ammo fits well it shoots a LOT better then my spudrifle ( http://www.spudfiles.com/forums/draguno ... ter,0.html )

Any ideas on what to shoot through a 15mm standard copper pipe? :P
i use plastic arrows that i make from self adhesive decorative stuff and wrap a nail in it or so.
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Unread postAuthor: wyz2285 » Fri Jan 14, 2011 3:08 pm

cool thing, i allways wanted to use a fire extinguisher, but i don´t know if they fix to any brass fittings :roll: .is it accurant?
first post :D
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Unread postAuthor: Gaderelguitarist » Fri Jan 14, 2011 5:35 pm

Well it certainly looks neat. I would have made the stock adjustable, as well as a cut off to allow that bolt to sit sideways while you aim.

Have you tried AA batteries?
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Unread postAuthor: nature-boy » Fri Jan 14, 2011 7:33 pm

Good work! Especially if that is your first pneumatic, is it?
On the pictures it looks like a hammervalve as a main valve, there are not that much hammervalve guns here. :)

How about the performance?
I would use Nail-Darts as ammo, what did you use until now?
The gun seems to be quit long, what is it's length exactly?
What is the big barrel shroud for? Is it just for aesthetics/ergonomics?

A lot of questions...
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Last edited by nature-boy on Tue Jan 18, 2011 6:56 am, edited 1 time in total.
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Unread postAuthor: django » Sat Jan 15, 2011 1:30 am

Its hard to see how the gun is triggered and how you made the hammer valve? can you please comment on this to clarify??.......
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Unread postAuthor: human » Mon Jan 17, 2011 12:33 pm

Thx guys!

i attached a diagram of the system.

The trigger is made from a bend piece of metal and a piece of a beerbottle opener.. The valve is firmly closed by a big spring, so the spring behind the bolt is powerfull as well. i took it from a hi-hat stand.

I still find that paper or plastic arrows are the most accurate. if they fit tight they are very efficient and shoot though my (thin) wall even without a nail in its tip!
AA batteries don't fit well unfortunately..

nature-boy wrote:Good work! Especially if that is your first pneumatic, is it?
On the pictures it looks like a hammervalve as a main valve, there are not that much hammervalve guns here. :)

How about the performance?
I would use Nail-Darts as ammo, what did you use until now?
The rifle seems to be long, what is it's length exactly?
What is the big barrel shroud for? Is it just for aesthetics/ergonomics?

A lot of questions...


Yup its my first pneumatic :D i used nail darts, and everything i had laying around in my house, including a piece of Gouda cheese (rubbery stuff that sealed well ;) )

it is pretty accurate and powerfull if the ammo fits well..

the barrel is 50 cm long and the entire thing is 104 cm. and it weights a ton. because of all the metal parts..
The carbon tube around the barrel is for aesthetics and strenght. It also carries the bottle underneath it.
i was inspired by this thing..

Image

Cheers![/img]
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Unread postAuthor: more_eggs » Tue Jan 18, 2011 3:28 am

You get 20 shots out of around 200psi.. Must be damn efficient.. What is the power like? Shot at anything solid that you can sort of paint a picture for us?
It looks damn nice.
With your hammer valve setup, how good is the seal between where the yellow piece runs back into the black piece? Im worried if I tried to implement this with an o-ring detent setup it might not shoot, and and the air would just seep through the seal there..

Overall looks awesome man, good job
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Unread postAuthor: jackssmirkingrevenge » Tue Jan 18, 2011 4:48 am

more_eggs wrote:Must be damn efficient.. What is the power like?


My guess a price in power is paid, in the sense that it's more "economical" than "efficient".
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Unread postAuthor: nature-boy » Tue Jan 18, 2011 7:39 am

Did you build the hammer-valve yourself?
Because I can't tell that from the pics. Do you have better resolution ones, especially from the valve?
Is this a "hammer-spring-adjustment-screw" in the back of the stock?
If yes, I like it! Is it accessible from the back of the stock, without removing the wood-part?
If you like that "economical" aspect, Jack mentioned, and you don't care that much about power, maybe it would be a good idea to add a regulator to the tank, it should not be hard to get one that can handle 200psi easily. That would give you even more shots and make them more consistent.
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Unread postAuthor: human » Wed Jan 19, 2011 6:01 am

[youtube]http://www.youtube.com/watch?v=_stvfN0Uh3M[/youtube]

i made a small video to show you more details!

Yes the screw is for adjustments to the spring ;)

I really like to have a regulator! where do i buy this?
i just discovered dealextreme.com and i purchased a cheap scope. ships to holland for free! :shock:
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Unread postAuthor: Gun Freak » Wed Jan 19, 2011 5:53 pm

Me likey... were the threads on the FE standard?
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Unread postAuthor: ramses » Wed Jan 19, 2011 10:23 pm

I think your hammer valve might actually act as a regulator. When pressure in the FE is high, the valve reseals more quickly than when pressure is lower.

If I am off base, you can check ebay, amazon, or harbor freight (or the Holland equivalent) Perhaps even dealextreme.com
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Unread postAuthor: saefroch » Wed Jan 19, 2011 10:34 pm

ramses wrote:I think your hammer valve might actually act as a regulator. When pressure in the FE is high, the valve reseals more quickly than when pressure is lower.
That's the idea behind using a hammer valve in a PCP gun.

The Source of all Knowledge wrote:The pressure of the spring is constant, and the pressure of the air decreases with each successive shot. As a result, when the reservoir pressure is at its peak, the valve opens less fully and closes faster than when the reservoir pressure is lower, resulting in a similar total volume of air flowing past the valve with each shot. This results in a a degree of self-regulation that gives a greater consistency of velocity from shot to shot than would otherwise be expected. A well-designed PCP will display good self-regulation properties, meaning good shot to shot consistency over a range of pressures as the air reservoir is diminished.
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Unread postAuthor: jackssmirkingrevenge » Wed Jan 19, 2011 11:14 pm

saefroch wrote:
The Source of all Knowledge wrote:...


Actually I had phrased it a bit more succintly :P :D

Seriously though, this factor in hammer valve pneumatics is well known. For the same reason, pressure in such a pneumatic is not necessarily proportional to power, because it increases resistance to the valve opening. Most hammer valve PCPs have a "power curve", with a "sweet spot" around the middle where power is at its highest.

As an example, here's a chrony string of 6 x 10 round magazines from my Daystate, staring with a 230 bar fill (using 16 grain JSB pellets, data in feet per second):

813, 821, 824, 825, 826, 832, 837, 839, 846, 843
850, 852, 856, 857, 856, 863, 864, 866, 871, 872
878, 878, 879, 886, 886, 889, 888, 889, 886, 887
895, 893, 890, 889, 887, 884, 882, 878, 876, 874
878, 874, 871, 865, 862, 860, 859, 858, 853, 847
846, 844, 837, 831, 823, 821, 811, 801, 798, 793

As you can see, even though the pressure is constantly reducing, power goes gradually up to the "sweet spot" reached at the fourth magazine, then starts going down again.
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Unread postAuthor: human » Thu Jan 20, 2011 5:23 pm

Aha so my hammer valve is a bit self regulating! Genius!
That might explain why the first couple of shots with a full tank were very crappy.. (valve didnt open well). i adjusted the spring to compensate for this, so it always opens the valve with plenty of power. Great info guys!

Me likey... were the threads on the FE standard?

Do you mean how it is attached?

I really like how this project worked out :lol: The fire extinguisher provided both the tank and the valve mechanism, and even a pressure meter. For use as an 'indoor' gun it provides enough power.

I hope someone will make one too and post the story on this forum.
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