I built this gun to test spark plugs and sparking igniters at my work. It uses 4-6 volt lantern batteries in series-parallel to achieve 12 volts to drive a standard car ignition coil.
Step 1: Batteries
The batteries are as simple as the circuit shows, just wire them together as a series parallel circuit. You don't have to use the 6 volt lantern batteries, you could use two 12 volt batteries such as those from certain Power Wheels or emergency lighting systems. Or you could always go full scale and just use a standard car battery, but this designed to be easier to carry and lighter. I do not recommend using smaller batteries such as C, D, or god forbid AA or AAA, as the current draw could prove explosive
Step 2: Relay and Capacitors
This gun uses a relay with two capacitors to act as the points system and condenser, so if you build this you will hear the relay chattering when you push the switch because it is constantly pulling in and dropping out instead of trying to keep the coil on constantly which wouldn't work for this system. I used two 350 VDC 100 µF capacitors. The relay is 12 volts. I know my wiring looks a mess because I put this together at work with the material I had.
Step 3: The Gun
The gun itself is made from the casing of an old soldering gun I had laying around. The wires coming from the coil and the relay are attached to copper rods that are secured into a block of wood with the other end being attached to a spring and a solid plug. The assembly is red because I sprayed it with an aerosol version of glyptol, an insulating coating used for breakers, motors, and transformers, because I was having some discharges at the wooden block. You could probably alleviate that by placing the electrodes farther apart. The switch is a standard momentary push button, I had originally started using the switch from the soldering gun but it fell apart too easily, the switch is run from the battery as the schematic shows and you could run it back down to the relay like in the schematic but after some toying around I realized it was easier to splice it into the wire running to the electrode, where it was going to connect anyway, and saving myself more wire. The box everything is in was something that was just thrown together, there is a top with a handle on it that I forgot to take a picture of but it's smaller than a car battery and quite a bit lighter.
Step 4: Hazards
This is a high voltage instrument. I don't even have a testing device to see how high mine goes and because of how i acquired my ignition coil I'm not sure what it's supposed to be rated for. On average an ignition coil can be anywhere from 15KV up to 50KV. If you've ever held a spark plug wire while someone turns a car over you will know what it's like to be shocked by this gun, I won't say it doesn't hurt and I won't recommend you to try it to see how it feels to you, but I've become slightly desensitized to this one because I've accidentally hit the button too many times. I have the gun itself and most of the cord going to it wrapped in several layers of electrical tape, partially to prevent any arcs in unsuspecting places and also because the plastic of the gun has started breaking and this is what holds it together until I can get/make a better housing. Good luck to you