Have you done anything to the inside of that gun? If you can still open it I would suggest making the air seal better and possibly affixing the grey turrett holder to the gun.
So instead of having 3 layers of moving internals, you simplified it so the breech ''advances'' by moving the outer layer/cover instead of an internally rigged ''bolt''?
Oh this is bad, the practical Nerfer in me says, put a breech on it, cover the heat induced hole in some epoxy, finish it off with a badass pj and some lepard tights an take that axe to war.
Holy wow Sooth, I think Brawndo (<--You Tube it) is no longer the coolest thing on earth.
On topic, even though this is so impractical, please Blue, please add this to the directory!
If you didn't know yet that ''little rubber piece'' is an O-ring, you can most likely buy more at your local hardware store, they would most likely be in an isle with gaskets or pluming fittings.
Good first write up! Could be a little more descriptive, but hey nice job. Griff