One of the biggest challenges of this project was to create a recoiling system for the gun. Ideas have been going in all sorts of direction, but now we have finally landed in something that works. Less is more, and we were fortunate to get hold of an old pinball solenoid. On top of that we use a power cube and an Arduino controller transistor. The result is a controlled, magnet propelled piston, awesome! : D
We also replaced the iron core that came with the solenoid for rare earth magnets, to see if that would give a little passive boost.