This is how to make an awesome gluestick cap firing device.
The Ingredients:
1x Gluestick
1x Good spring (That will fit inside of the gluestick)
Good strong glue (not from the gluestick!)
Fimo (modeling clay that can be baked to harden) OR some piping (also has to fit inside of the gluestick)

Step 1: Remove the Glue

Twist the base of the gluestick until you can pull the glue out, along with the small piece of plastic used to move the glue. You'll want to use a knife, or whatever you can lay your hands on to get all the bits of glue out from the plastic bit, making sure you get it so that it's not sticky, leaving it to dry might help..

Step 2: Craft the Fimo

Now that you have removed all the glue you need to re-insert the bit of plastic into the gluestick, and twist the base until it has reached the bottom. Now, take your spring, and pop it into the gluestick, if it is so long that it sticks up ~8mm-1cm over the top of the rim of the gluestick, you will want to skip this step.
For everyone else, Take the Fimo, and make it into a small tube, with a hole big enough for the centre piece in the gluestick to get through. Using some more fimo, attach the spring, and then bake the whole thing in the oven.

After you have baked it, and found that it doesn't fit over the central peice in the glue stick, (as my second and third attempt did) use a drill and drill through the fimo, until large enough.

Step 3: Glue Together

Using some strong glue (I used araldite glue) stick the Fimo+Spring piece onto the plastic bit from inside the gluestick, making sure no glue covers the hole.
If you did not use the fimo, because you had a longer spring, glue that to the plastic bit.
Then leave to dry.

Step 4: Finished!

Take the spring/Fimo/Plastic bit, insert into gluestick, twist base to lower it into the gluestick, add cap, and twist base to fire!
Now, remember not to fire it at too many people, or they might get annoyed!

If you have any questions/ comments/ complaints I would like to hear them, as well as any modifications!