Voltage is very important. I = V/R. More voltage = more current. 'Nuff said. Lets say the coil has a resistance of 100mOhms. For current, that's 120/.1=1200A. If you used 12V, you get a much less impressive 120A.
Secondly, a cannot stress this enough: Charge up the capacitor, and DISCONNECT IT FROM EVERYTHING EXCEPT THE COIL. When firing the coil gun, nothing should be hooked up to the wall. However, the lightbulb is a good idea when charging the capacitors, as the capacitors probably have very low ESR, and would likely try to draw amps within the four or 5 digits. Even if it will only be drawing this for a few micro or milliseconds, it might be enough to trip a breaker. But if you just leave everything plugged in, well, you may as well just short your outlets out.
My advice to making fixing the coil is to add another layer, same gauge. Make sure you're hooking all the coils up in parallel. It sounds like there is too much resistance, which will lead to a slower capacitor disharge. 1 more layer will cut the resistance down, increasing discharge rate, and hopefully preventing any suction backward after the projectile goes past the center of the coil.