SpudFiles

I came up with a design similar to my last one, but it solves the problem of spewing propane out the side of the gun. I decided to go with using a chamber fan to draw in new air and to mix the fuel.

I have still kept the blow back propane injection design and this is why... The amount of propane let into the combustion chamber can be regulated very accurately by the combination of three things; the size of the hole that lets in the propane, the pressure at which the propane is regulated, and the strength of the spring that returns the piston. I will have to use a propane pressure around 20psi because I want to use it in cold weather and this regulator:
http://www.homedepot.com/webapp/wcs/sto ... =100554927 regulates between 0-20 psi.

Criticism of my design is welcome. It used Microsoft Paint to make the diagram (drawn to scale as always)

Hmm so the pump-action loads in a new round AND it covers up the air holes on ignition?
Possible.
But now the gun fires -> piston backs up -> propane gets in -> piston gets back to original position -> you shove the pump action forward -> gun vents -> shove pump action back -> fire

See the error?
propane injection -> gun vents
Not good.


Maybe also put the propane injection somewhere in the pump-action mechanism.

This design isn't pump action, but semi-automatic. When you pull the trigger back, it is connected to the barrel/hop-up system and the vent cover so the BB chambers while the vent holes are covered and then when everything is set to go, the trigger touches the igniter. All of this is accomplished with one pull back of the trigger. When combustion occurs, the BB shoots out while the piston is moving back to let in propane, then returns. While the piston completes that action (which should be very fast), the trigger moves back forward (by spring), opening up the vent holes and letting a new BB jump up into the chamber.

Well, its basically pump action which also triggers, but just because of the small scale of the bb caliber, the path is short enough to be a finger trigger.

But then again, the flaw is that your first inject fuel and then vent.
You will simply vent out your fuel.

Oops My mistake. In my excitement over having a design that "works", I ignored a very crucial flaw that you pointed out. Well... never to fear, I will come up with a new design!