As people have said, you'll need a lot more power. A good rule of thumb with magnetic accelerators is: if the cap bank can't blow you across the room, the coil gun isn't going to work. The whole project is a bad idea. Be careful, use bleeder resisters, insulate bare wire, take all usual high voltage precautions, etc. Also, get a pair of goggles that block UV. A good size spark puts off a fair amount of hard UV, and having cateracts before you hit 30 would suck a lot.
Assuming you have a small gun, you can probably get away with using lots of photoflash caps in parallel. If you ask nicely, many pharmacy photo counters will let you take away used camera bodies by the bagful(at least back when I was playing this game). Pull all the caps out(carefully) and solder them onto hefty copper wire. With the fairly low voltage (c. 300v) on photoflash caps, you'll need very, very low resistance coils. This means using heavy wire all throughout the circuit. The tricky thing about coilguns is getting the discharge to be fast enough. Ideally, you want all the energy to be released at once, or at least before the projectile has made it more than halfway through the coil(otherwise the coil will slow the projectile down again). Typically, as well, mechanical switching is too slow.