loading

Assistance needed for coil gun design. Any help appreciated.

Hello. Frequent reader, first time posing.
I have been working a coil gun project for awhile now, nearly a month.  Originally I was using a pre made coil I took out of a fan.  The coil itself is roughly 42 gauge wire, with roughly 8-10 layers, and an inch long. At first I was using flash camera capacitors (300v @ 80uf) and flash camera circuitry to shoot a screw or nail through a pen tube. More recently I have been using a 12vdc to 120vac converter rectified to about 200vdc as a charging unit.  I also obtained some high voltage electrolytic capacitors (450v @ 820uf) that charge after about 2 or 3 minutes.
After messing around with with the completed assembly, using a push button to short the capacitors across the coil, I realized that the wire coil itself was limited by its gauge and size and the full potential of the capacitors was not being maximized. So I ordered a spool of 63 feet 16awg magnet wire to make a larger coil for a more powerful and efficient design. So today I wrapped a coil around a 1cm clear plastic tube that was about 4cm long and 3 layers thick. The coil itself has a very low resistance.
I hooked up a 200v 470uf capacitor to the coil and the charging circuit and when I fired my push button was welded shut. After that I was just shorting the capacitor across the coil to fire ferrous projectiles, which resulted in a rather large spark where I was shorting it. I noticed lower efficiencies compared to the other coil, which I'm sure has a great deal to do with the the energy the spark waste.
So question number one: does anyone know what type of firing switch I would need to handle roughly 500 volts at 10(ish) amps and where I could find one.
My objective is to achieve maximum kinetic energy with a 10mm x 30mm projectile. I have chosen to use a clear tube to eventually have a optically triggered multi-stage design. From research I have concluded that a coil should be 33% to 50% larger than the projectile, so my coil length has been established. I would like to know how many layers I should use to maximize the first firing stage with a capacitor rated at 450v 820uf and a coil that is 40mm long.
Sorry for such a long post, but any help is greatly appreciated.