I have been studying how the AR's gas system works. I even dug up Stoner's original patent and read it. I think I understand how it it works now for the most part, but one thing I don't understand is why there are gas rings to seal one end of the expansion chamber in the bolt carrier while the stem at the rear end of the bolt simply slides within the bolt carrier without a similar type of seal. Seems like it would allow gas blow-by at this point that would escape around the firing pin flange and into the receiver. Is there a reason why a second set of gas rings weren't used to seal the bolt stem? Same thing with the carrier key and gas tube. Until the bolt carrier slides back and opens the 2 vent holes in the side of the carrier, the high pressure would seem likely to cause gas leakage at this point without some type of ring seal. I am also wondering what the purpose of the rear vent hole in the bolt carrier is. This hole connects to the passage that the bolt stem slides in. Is this to allow the blow by gas to escape?
Stoner's patent showed a slight variation of the system that actually used the bolt carrier to seal off the gas tube from the expansion chamber after it had moved backward a short distance. Similar to a two-cycle engine. Not sure why it wasn't used in the final design.
After looking at the design, I was struck by how similar it is to a normal piston engine. Although I think that the exhaust gas is better sealed and routed to the outside world in an engine than in the AR. Seems like it could be made to work cleaner, though, without giving up the advantages of the direct-gas impingement system. Anybody know how to design an exhaust manifold for an AR? An AR with headers, what could be cooler than that!
I suspect that without some leakage the high gas pressures would destroy the gun. If it were truly sealed, the only exhaust port would be the gas tube leading back into the barrel - which I think would foul the barrel quickly and destroy accuracy.
Seal it and design an exhaust port? Nothing wrong with that that I can see - except on where to place it. Concentrating all the exhaust in one place could be hazardous to the shooter and could damage the gun if it were blocked off.
Just some thoughts...