Warning! This is only a concept, 3D printed plastic is not fire proof and I accept no responsibility for injury caused by this cotton bud gun.

I printed this as proof of concept, it uses a mini hob lighter (available on EBay) to launch a cotton bud (ear swab) cut in half and put down the barrel cotton end first (slightly dampened). I printed the chamber separate to ensure no supporting structure was inside, before gluing it to the bottom of the gun using PVC Pipe Cement (type used by a plummer). The barrel may print with support, I used a thin screwdriver to push this out.

When the glue is was dried, I put the half ear swab cotton end first (after a little lick) in the barrel, put the lighter in the chamber hole, carefully squeezed the trigger for about 8 seconds to let some gas in (not all the way as to light the lighter), then aimed and squeezed the trigger all the way in to activate the piezoelectric ignition.

Vids...

https://www.youtube.com/watch?v=wrvnS26oxhs&feature=youtu.be

https://www.youtube.com/watch?v=Y5Xo0iH5WVo&feature=youtu.be