So, its very simple: You need 2 valves in this simple system and a little overdimensioned combustion chamber ( the pressure shuts first the valves and then the pressure has only one way: out of the barrel.
The first valve is simply a blowback valve. it closes in one direction. It is diagonal, because it only shuts of for a very short time. mostly open.
The second valve ( i will add pictures) is a simple valve, that shuts at overpressure. Its open for leaving the mixture in, but once there is pressure after ignition, it closes. This 2 Valves are the miracle.
It is very loud. And you can see on the pictures: the most darts explode and only the rubber hits^^ Foam works like a shell^^
I will make Video outside.
