Captainbertie, techno dummy at this end has read through some other forums so hopefully here a picture of the recoil mechanism and the wiring. The pictures show the gun run out and recoiled. The recoil pulse from the tracks is just enough to turn the motor behind the righthand cog. This moves the link pulling the barrel back far enough to open a micro switch in the mantle (mounted by the screw visible in the forground). This switch then enables a larger current to the recoil motor making the cogs turn with enough power to overcome the recoil spring and push the barrel forwards again. This in turn closes the micro switch cutting power to the motor and resetting everything for the next shot.

Where I messed up was the diode on the red wire under the barrel was not high enough to prevent a 7 volt spike getting back to the pcb ooops! The red wire goes back to the black wires which in turn are soldered to the recoil puls pins on the PCB.

For my next attempt I am trying to make a circiut that will take the recoil pulse and use this to open an electronic rather than mechanical switch. This should enable me to make the recoil motor work for a set time period independently of the main PCB and reduce the risk of frying andother board.

Only snag is going back to work this week kills off any spare time for playing.....