Switching high current and high voltage for coilgun
450V 100A? Wow. That sounds like you're using a capacitor to power each coil? Also, with that kind of energy, I believe it would put holes in brick walls.

Keep in mind that the larger the ratio of number-of-coils/energy-per-coil the more efficient your coilgun will be. Using capacitors may not be the best idea if you are looking to make an efficient gun. Most hobbyist coilguns have an efficiency of 1-2%. Depending on the mass you're accelerating, it may be a better idea to use more coils or more turns per coil and a constant current source rather than a capacitor. Keep in mind that with a capacitor, you are going to have to seriously think about heat dissipation.   

That said, I don't know about anything up to 450V. My experience with large amounts of electricity stop at about the same level as wall current. I would suggest looking here though. He seems to have some stuff on capacitor driven coilguns.

This might help also.

Good luck, and don't blow a hole in a wall. ;)