The idea is to have the piston connected to a threaded rod in a tube that controls the filling and firing cycle. It will be filled and fired the same way, filled through a hole in the end plug (red) and backpressure released to initiate the firing cycle.
The barrel seal itself is a rubber stopper (black) drilled through for the threaded rod. As pressure is applied through the rear of the tube, the floating piston (orange) pushes the whole assembly forward until it is past the holes in the power tube (white). Note that the floating piston is free to move axially along the threaded rod. The spring would be compressed slightly at that point to ensure there is forward pressure on the stopper keeping it in the barrel (green) before the chamber pressure takes over that job.
Fill Position:
When filling is complete and pressure stops increasing, the floating piston would be pushed back by the spring to seal the chamber from the power tube. Once the backpressure is released, air pressure from the front of the tube would push the floating piston and the entire assembly towards the rear of the cannon, allowing air to flow down the barrel.
Fire Position:
That's the idea, anyway. Any concerns before I start building it this weekend? Suggested changes?
Thanks for your time.
