Originally supposed to form the armament for a collaboratorive Automated Turret.

The premise was to use an SPWM inverter, created during the course of the spherical drive project, in order to produce a 12V pseudo-AC signal from a 12V battery; convert that to 230V AC via a transformer, pass it through a full-bridge rectifier and charge three 250V 1800uF capacitors.

The first capacitor would be discharged with an external button press; via a cascaded transistor, thyristor set-up. The subsequent capacitors would be discharged in the same manner the only difference being that the trigger would not be external, rather their discharge would be prompted by two light-gates within the barrel. Each light-gate would trigger as the projectile obscured the LED light source from the photoresistor. 

In this manner it was hoped that a three stage coil gun could be created. Some pretty rough and very idealistic envelope calculations implied that each capacitor had the potential to give the ferrous projectile approximately 50J of energy.

A ferrous project with a diameter of 5mm and a length of 20mm would have a mass of approximately 10 grams. In a perfect world the 3 stage coil gun, as described, would emit projectiles with a theoretical exit velocity of approximately 130ms^-1. Or about 300mph.

Certainly enough to hurt or even kill somebody, but nowhere near an actual fire arm. For reference, an air-rifle might be around 40J of KE and an assault riflle around 3KJ. Certainly enough to knock down some cans though! Destroy some fruit, y'know that kinda thing.