MrCrowley wrote:Any reason you want to use an o-ringless design? Apart from reducing maintenance and possible things that could go wrong, are there any other reasons?
Nope. You nailed it for the most part. I figure fewer things to go wrong, no maintenance, a piston that moves more smoothly, and maybe even a slightly lighter weight piston since the grooves for a labyrinth seal need not be as deep.
Edit: I'd rather you go with the labyrinth method over o-rings as it would bring about a new 'development' in hybrid construction.
In the 'development' sense I'm doing several things that I think are new although I confess that I've not done extensive reading to ensure of that. Maybe others have done it this way. I dunno. I'm just doing it this way because it seems the "right" way to do it.
Concept of operation....
0) Gun's basic configuration appears to be that of an old school pneumatic coaxial. There are some differences, but that's close enough for this conversation. Also note that there are check valves connecting the pilot area to the combustion chamber (with flow being allowed from the pilot to the chamber).
1) Barrel sealing piston valve is open. Using a metering pipe, propane is injected into the pilot volume. (If all goes well) the propane drives the piston forward to close the valve and more or less just sits there in the pilot although some will certainly leak to the main combustion chamber either around the labyrinth seal or through the check valves.
2) High pressure air (also from a metering pipe), is injected into the pilot volume. The air mixes with and drives the propane out of the pilot area and into the combustion chamber. At first, the mixture in the pilot will (obviously) be very rich, but as the process continues you should end up with essentially air (yes, there will be a bit of contamination) in the pilot volume and a combustible mixture in the combustion chamber.
3) From there, operation is just like any other valved hybrid with one exception... As the piston moves backwards as the valve opens, the pressure in the pilot area will obviously increase. At the same time (or ever so slightly afterward if you want to split hairs), pressure in the chamber will be falling. When the pressure in the pilot exceeds the pressure in the chamber, air from the pilot is vented into the chamber thereby giving a teeny tiny, probably not even measurable boost to the power of the gun as the energy contained in the pilot volume is sent down the barrel rather than being wasted.
Mind you, the "pilot boost" is minimal at best. I just figured, "Hey, why not vent it somewhere where it *might* be useful?" And as a bonus, the gun should be ever so slightly quieter to the user.
4) Oh, and the whole mess will be quasi automated so that while you're aiming/shooting, the metering pipes are refilled.
edit: Upon a re-read... Two more points....
a) When I quoted you, I meant to emphasize the "o-ring required" not the "difficult to build" aspect of your quote. I agree that o-rings aren't difficult. I disagree that they're required.
b) Sadly, I don't have regular access to a lathe and such so construction will take a long time (gotta call in favors and the like). I figure I'm at least a year out even if it won't take but 20 man hours to build.
They (o-ring hybrid pistons) are not exactly difficult to build if you have a lathe or similar machining equipment either. 
