See my design on the previous page
I don't understand it, looks like the pressure inside it would push it to the right as soon the pressure would increase and stop the refilling.
And the reloading mechanism is missing.

I think this is what you mean? (see attachment)

I'm not sure what you mean ...

Why is it lacking power?
The orange part is one piece btw.
So I have to make it stay in place when firing?

Define handheld

Tiny bit smaller , 4 feet?

airgun pellets, .177 or .22, semi auto at atleast 500 fps, handheld

How about this?

This is the piston of the QDV
What's your plan for stopping it kicking back violently on firing?
I was thinking about a piece of rubber in the spring..

That said, pulling them forward with a spring (so the user's hand is not directly implicated) would help that.
What? sry, it's 1:15 AM here :P

So... Ready for the trashbin.
Thx for the replies and saving me a lot of time and money building something that won't work

I can't see how this counts as a QDV.

This is the piston of the QDV
http://img708.imageshack.us/img708/6347/pistonc.png
Here you can see the air pushing the piston back when is fires. http://img25.imageshack.us/img25/5451/semiautopneumaticfiring.png

@ JSR, I still see some difference in ...

http://img827.imageshack.us/img827/6978/semiautopneumatic.png
This is just a pneumatic, but loading, firing and refilling is done in one stroke.

Charged:
http://img585.imageshack.us/img585/3240/semiautopneumaticcharge.png
Firing:
http://img25.imageshack.us/img25/5451/semiautopneumaticfiring ...

Fnord wrote:I can't think of an easy mechanism to do the latter right now because I'm tired. JSR where are you?

I found one, just don't know if it really is going to work:

Thx to Fnord for the vacuum reloading idea:
http://img638.imageshack.us/img638/9131/semiautocombustionvacuu.png
http://img825.imageshack.us/img825/9131/semiautocombustionvacuu.png
Still one problem: When the air cools down, it sucks back the bolt. I think thats gonna work. BUT I also want it to ...

al-xg wrote:Venturi nozzle for fuel mixing...

I have one from a broken jet lighter. Would it inject the right amount of air and fuel?

Would the check valve at the back of the bolt do the same job?

I don't think you'll get a cycling action with this design, however you gave me a brilliant idea.

You don't need a gas-piston. Make the bolt fairly heavy, and put a spring behind it.

The vacuum that forms after the shot will suck the bolt back.

You won't get every last bit of air out, but you ...

Well, back to the drawing board

EDIT: New Idea: Bolt action. Manually cycle bolt but still auto refueling and fresh air:
Cycle Bolt -> pull trigger -> BOOM!!! -> Cycle bolt -> pull trigger -> BOOM!!!

No problems about gas port position etc 8)

It works like an ak47: http://www.youtube.com/watch?v=wX3vIW9MkNk
Gas pushing back the piston and reload.
http://img409.imageshack.us/img409/3628/semiautocombustion.png
BOOM!!!
http://img832.imageshack.us/img832/2075/semiautocombustion2.png
Darts won't fit in a magazine like thaht. So I'll use ...