This is roughly as powerful a coil gun as you can make using a standard mains switch. To make a more powerful coil gun you will need a higher rated switch, preferably solid state.
Through much research I found all the Variables that affect the efficiency of a coil gun:
Length to diameter ratio
Number of layers
Thickness of wire
Current Pulse length
Switch bounce and resistance
Capacitor Voltage and Capacitance
Overall wire length and diameter used.
Also there are several ways to increase standard performance using:
Optical, Inductive or Physical Triggering
Step 1: The Plan
I had some 6mm steel bar, some 6mm plastic pipe, a micro switch and some enamel coated wire as a starting point.
I took apart 17 disposable cameras and soldered the capacitors in parallel to form a capacitor bank of 1360uF 330v which using E=1/2CV^2 gives a stored energy of 73J.
I used one of the camera circuits as a charging circuit by removing the flash, removing the trigger switch and soldering the charge switch closed.
I then used an old mains PSU switch as a charging switch although any switch will do. The whole circuit was covered thouroughly in insulation tape and put in the only plastic box of the right size I could find at the time; An empty Bertolli spread box.
I wrapped a coil out of 26AWG enamel coated wire 30mm long and 7 layers thick. This is because the coil should be the same length as the projectile and the projectile should be five times longer than it is wide, hence 5x6=30. The number of layers is dependant on wire thickness and capacitor bank size and voltage. The thinner the wire, the smaller the bank, the less layers. wire too thin will impede flow and maybe burn out. Wire too thick will mean you have less coil density than is potentially attainable.
Simulations ran well after the device was constructed reveal this isn't an optimal design and there is some 'suck back' as you can see on the graph when the turquoise line falls bellow the axis suddenly.