SpudFiles

I've been lurking here for about 2 months now, and in that time have built a couple cannons, largely thanks to the information on this site.

Lately I've been wanting to build a high powered airsoft gun. Whilst scouring the forums for ideas I came across JSR's Rattlesnake poppet valves. They seem to be a powerful and efficient design but in my application they had two drawbacks: They need a blow-forward bolt or some other means of sealing the breech, and the barrel exits from the side of the valve.

Basically it is the poppet valve and blow forward bolt combined into one. Once the chamber reaches a high enough pressure the piston unseats, and like any piston valve due to the larger exposed area is pushed back. This closes the bolt at the same time. The now open piston releases air through the bolt and out the barrel. Once the pressure drops low enough the piston reseals and the cycle restarts.

It seems to work in theory, or am I missing something?

(edited to fix pic)

you may want to fix the image link.

the popet valve should work but the blowforward bolt might have some problems. a popet valve doesnt move much when it fires. this means that the bolt also wont move the correct distance to make the blow forward bolt seal off the mag. to do this you could use a pison with two diffeent diameters and anougher oring. this would cause the piston to move the distance before "popping"

<a href="http://s696.photobucket.com/albums/vv32 ... poff-1.jpg" target="_blank"><img src="http://i696.photobucket.com/albums/vv32 ... poff-1.jpg" border="0" alt="Photobucket"></a>
not a very good drawing but i think you get the idea
not to scale and the piston could be considerably smaller to reduce weight
opps i seem to have forgotten to add a spring and a oring on the larger part of the piston.

The image shows up for me so I'm not sure what's wrong there. If you could see it it would explain what's different about the valve. Instead of having a separate bolt mechanism the bolt is actually part of the piston. So when the piston pops open it is closing the bolt.

I can see the pic too.
Aren't the two pics basically the same thing? I don't think c11man understand what you're trying to do.

After taking a closer look, I see what you mean about the valve not moving enough. It' shouldn't be too much trouble to make a piston with two diameters like you suggest.

I understand what hes trying to do. and the two pics look the smae at a glance but on mine the piston moves a little over 1/4inch before the vavle "opens". this lets the mag be complety sealed before any air is released.

of couse you can see the pic

(edited to fix pic)

It seems I came up with a similar solution.



The theory seems sound but never built a working prototype.

jackssmirkingrevenge wrote: The theory seems sound but never built a working prototype.

Well, there's only one way to fix that!

Insomniac wrote:Well, there's only one way to fix that!

True... but these days, I'm more into detents than reciprocating mechanisms...

In my opinion it's not worth the hassle to make a reciprocating bolt seal when it's so easy to make a removable magazine that seals with negligible dead space anyway. Just get some of the same tube you're using for a barrel and find an o-ring that fits over it and make a female o-ring groove and there you go.