SpudFiles

http://www.flying-pig.co.uk/mechanisms/ ... ngine.html

Notice the rod that slides back and forth on the main piston, if that were made out of a hollow tube, and had a perforation that would open up at the end of the main piston's travel, it would empty the chamber every time the piston moved to one end of the chamber. This would make a double-barreled, fully automatic gun.

Hope that makes sense.

If it were perforated, the steam would escape prematurely, and it wouldn't push the piston through it's full travel, (i think).

I'm saying that the bolt would be open once the piston has reached the opposite end of the chamber, the steam/air would escape at this point anyway if it were a normal engine.