SpudFiles

Well, After abandoning spring piston air rifles, I am looking into single action air rifles. Pretty much they are air rifles that you have to only pump ONCE to fire. Does anyone know anything about these? I was trying to design one but I got stuck on how to seal the pump. Any links, pics, or advice is appreciated. Thanks!

I recommend searching the internet for information on the Parker Hale Dragon, one of the better known single stroke pneumatics.

It probably wouldn't hurt to research the FX Royale too, because that's a (multi-shot) PCP with a built in pump.

And I'm not quite sure what you mean by "seal the pump". The only thing that seems to make sense there is "O-rings", but I'm sure you knew that, so I have to assume you're talking about another problem.

Look at the crosman 781 VERY accurate gun I loved it until I broke it haha.

A single stroke pneumatic is really not all that different from a multi stroke pneumatic.

The major functional difference is the lack of a check valve in the single stroke pneumatic.

Parts diagrams for the 781 can be had here;

http://www.crosman.com/pdf/manuals/cros ... 81-EVP.pdf

here is my partial design, what do you think?



and by the way all of you who have posted so far, thnaks, I used those designs for help.

A few items that pop to mind;

You will need some way to hold the piston closed once you compress the air in the chamber.

A sprinkler valve has a (comparatively) large volume on the downstream side. In combination with what looks to be a fairly small chamber charged to low pressure, this will substantially lower the pressure available to accelerate any projectile.

Low pressure in combination with a small bore size will fail to impress power wise.

I would recommend replacing the sprinkler with a blowgun, small piston valve or 1/4" qev.

This would remove most of the valve associated dead space, and improve performance, while still keeping it simple.

Finally he sees the light

Gippeto wrote:You will need some way to hold the piston closed once you compress the air in the chamber.

A check valve should do the trick

A sprinkler valve has a (comparatively) large volume on the downstream side. In combination with what looks to be a fairly small chamber charged to low pressure, this will substantially lower the pressure available to accelerate any projectile.

Low pressure in combination with a small bore size will fail to impress power wise.

Not to mention it probably won't seal with such a low flow.

I would recommend replacing the sprinkler with a blowgun, small piston valve or 1/4" qev.

Agreed 100%, for small calibres a blowgun is great, with this setup at just 100 psi I can do this

maverik94 wrote:Pretty much they are air rifles that you have to only pump ONCE to fire.

Why the insistence on a single pump? The Parker Hale Dragon which Rag mentioned could do a respectable 12 ft/lbs with a single stroke but its a long and complicated rifle. Why not attach a shock pump directly to a blowgun if you want a portable setup? One pump will still give you some power, but if you needed more you could always take it higher.

wait...wouldnt the friction of the piston hold the piston in place? Also, I agree that the sprinkler valve is overkill, bit If I used a blowgun trigger, that would have a tiny airflow, which would reduce the power right? Also, i thought that qevs only came in 3/4" sizes for paintball.

EDIT: Ok, how many pumps would it take a shock pump to take the inside of a blowgun valve plus a little bit more to 100 psi?

Ok, Here is my revised design. This would be mounted on and in a wooden rifle body, but this is the bare bones idea.
Here it is:


What do You think?

You don't give enough information to make accurate calculations.

So, I'll take some liberties with your design to answer your questions.

A barrel with a 3/8" id and a length of 36" has a volume of 3.97cu.in.

A C:B of 2:1 would be a bit overkill, but manageable. This means you'll need ~8 cu.in. of chamber.

A 1" pipe nipple nine inches in length will put you close enough to that.

With a shock pump and an all metal launcher you could go a lot higher than 100psi, but, if you only want 100psi, a regular bicycle type pump will get you there much faster.

If your barrel is actually 3/8" od, you can reduce the chamber size substantially. (Still using a 36" barrel.)

For 1/4" id a chamber of ~3.5cu.in. would be fine.

For 5/16"id a chamber of ~5.5cu.in.

I had a setup like the one shown above mavrick and it sucked real hard, even 300psi it had no power

@ Carlman. Really? I've seen some videos of these that got shot through one side of a steel can at 100 psi. Actually, the barrel is going to be about 29" long. I'm still thinking of using a 3/8" brakeline for the barrel. Is brakeline measured by inner or outer diameter? I used GGDT to figure out the gun's performance, i wasnt sure what I lot of stuff meant, but with these values, I came up with a decent ammount of power. Are any of the values way off?



Also, about how long would it take a shock pump to pump up a 3/4" long 1/2" chamber to 120 psi?

This is a model of a (likely) blowgun setup with a 5/16" barrel id. using 9" of 1" pipe for a chamber.

It should give you a better idea as to how to enter values.

This may still be a bit optimistic, but not too far out.

so, in other words, This gun is gonna have very little power? Ok.....What do you suggest?

you could do something like my mini modgun...

36" blowdart barrel(.40 cal), attached to a 3/4" qev via a 1/2"comp to 3/4" npt fitting, and a blowgun to trigger.. according to ggdt with a 1.25"x 2" chamber at 250psi, you'd be shooting blowdarts at 800+fps...

maverik94 wrote:so, in other words, This gun is gonna have very little power? Ok.....What do you suggest?

First of all, the one modelled by Gippetto actually has fairly respectable power, more than 400% the muzzle energy of a typical CO₂ pellet pistol.

Secondly, a shock pump will let you reach much higher pressures so there's no reason to stick to 100 psi, if you go up to 200 psi for example then theoretically you should have double the power.