I needed a Christmas gift for a friend who dabbles in magic. Being an avid Make magazine follower, I thought Kipkay's excellent instructable would be perfect starting point.

Please note, the recipient of this shooter is an adult who respects fire. The following has none of the safeties/niceties you might expect from professional-grade equipment. I recommend you do NOT make this unless you are an adult with at least a smattering of common sense.

The idea was to make something he could hide up his sleeve to produce a flash effect at will without doing something as obvious as pressing a button. To activate the flash, he just has to raise his hand (which seems to be a natural movement if you're about to shoot fire from it).

I needed:

1 single AA battery holder
1 mercury switch
1 slide switch
1 1.5V glow plug
some Velcro
about 4 " of 1/2" thin-walled aluminum tubing
small piece of 1/4" plywood
flash paper
flash cotton

I got the tubing and glow plug at a local hobby store. The mercury switch came from Radio Shack about 20 years ago. The battery holder came from the Source. The slide switch came from a defunct Godzilla noisemaker. The flash paper and flash cotton came from the internet. The other stuff I had lying around.

Step 1: Construction and Wiring

Cut the aluminum tube to length with a hacksaw and grind the sharp bits off.
Wire one lead of the battery around the threaded area of the plug and solder it in place.
Use pliers to crimp the end of the tube around the plug. (Kipkay's instructable had a better method, if you can find 28 thread nuts, which I couldn't.
Mix up some JBWeld or similar and push it into the gaps around the plug. Don't use too much (the coil inside needs to be free and clear and the post needs to stick out the back end. I used locking pliers so I could keep them on for the 20 minutes it took to cure.
Hot glue your components to the board, making sure to leave the leads free of glue. I figured the safest method was to have the mercury switch open when the whole assembly was pointed down. The Velcro is under the tube to help angle it out away from the wearer's wrist. The raised end is filled is supported by hot glue.
Solder the remaining battery lead to the slide switch, then the other terminal of the switch to one of the mercury switch leads. Solder the other mercury switch lead to the protruding glow plug post. The idea is that the whole thing is wired in series - both switches have to be closed to activate the glow plug.
Everything is in place. Do one final test (you've been testing all along, right?), then hot glue over every exposed piece of metal (careful no glue gets into the slide switch - mine was open on the sides).

Glow plug test:

Step 2: Using the Fireball Shooter

This is the part I haven't mastered yet. The amount of flash cotton and paper, as well as how to crumple it and insert it, seems to be an art. Too little cotton and it won't ignite. Too much and it seems to blow out the paper without igniting it. Press everything in too hard and it won't ignite. Sometimes I get a big flash just over my hand. Sometimes it shoots a fireball across the room.

I load a pinch of flash cotton and a bit of flash paper into the tube so the cotton goes in first and push it down with a pencil or screwdriver (very lightly). I strap on the velcro, then point my arm down (so the mercury switch is open). I then turn on the slide switch. When I raise my arm, the mercury switch closes around the time my arm is horizontal. It takes a fraction of a second more for the cotton to ignite, so I can get my arm all the way to vertical before it fires, it I want to.

Loading the fireball shooter:

Using the fireball shooter: