SpudFiles

Well, a premixed tank at high pressure, a blowback valve between the chamber and the premix tank (Like those used in Acetylene/oxygen setups) and a regulator, then a ignition that makes one spark every xxth of a second and a piston valve.

Voila, auto-hybrid.

Ofcourse, you need to make a self operating valve, and probably a high flow relief valve behind the piston to let the valve pilot fast enough when the mix ignites behind the piston.

I would love to puzzle around with a bucket of fittings and some pipes to make some prototypes, but I lack the passion ATM.. I am scheduled to fix the other hybrid (WOW 500gm over mach one!!) in the course of the winter.

Really, there is absolutely NO reason why it is so hard and unreasonable to make a full auto hybrid. If you fueled your gun from a premix chamber and not a helium tank, and made a new valve you have done it.

Wrote too much here.

Pre staged is much safer than pre mixed.

Use two pre staging tanks in proportion to the desired mix, one for air, one for fuel. When the volume of both is dumped at the same time into the chamber, a metered volume of both fuel and air is injected and mixed. This reduces the possibility of a dangerous flashback.