evilgenius

If you just want to move the steel ball, you do not need a 400 volt capacitor. If you are building this for some stupid school project you could as well use a 4700uF 18v cap to power it. Use 2 9v batteries in series also make sure that the impedance of the coil is low or else the gun will be very weak. you also need to keep in mind that you have to switch off the current in the coil when the ball travels halfway through it in order to pervent the suckback effect. you can easily control this by using a 555 timer in monostable mode. instead of a mechanical switch i suggest you to use the TIP series power transistors or a relay. you still need to learn a lot in electronics before starting to build a coil gun. as for your fears of dangerous velocities, you do not have the proper capacitors or the SCR's needed to switch the current in the coil. i think that you still don't know how to use a transistor... I'm laughing my head out imagining you building a coil gun. you do not know the basics of a capacitor and a diode. quit trying to build something like a coil gun and concentrate on improving your basics first. your capacitor can store a maximum of 0.5*120*(10^-6)*400*400 joules of energy. that is too weak to build a coil gun that can even accelerate a steel ball to 1 cm/s