I also want to start by re-iterating his safety warnings as this device has risks related to fire, steam, pressure, metal-work, and projectiles. I recommend wearing eye protection during all steps and using common sense. I accept no liability for any risk in the manufacture or use of this device. Do not attempt to use power tools if you are not familiar with them and I don't recommend anyone under the age of 18 attempt to manufacture this device without competent adult supervision. Don't touch the barrel for a few minutes after it has been fired as it becomes extremely hot. Also, the soot will stain clothes/skin. Be careful with this thing guys.
I will leave the construction of the barrel/chamber assembly to robbtoberfest's design and will primarily focus on the design modifications which allow the fuel/heat source to be a "Zippo (tm)" brand lighter. The only modification I made to the barrel/chamber assembly is that I used "J.B. Weld (tm)" brand two part epoxy paste instead of solder. I find that it is less messy and I have limited experience with solder. The joints and air-tight seals of the "J.B. Weld" have held through all of my test firings. The farthest I have gotten it to shoot a plug his about 23 feet.
It works, but it has limitations. I feel that it would work well indoors with very minor drafts, but outside it is challenging to keep the flame on the chamber if there is any wind at all. Seems to take me at least a couple minutes of fairly steady flame on the chamber to get it to fire. I am not sure if this modification is faster/slower to fire. I think indoors it is probably about the same to a little faster to fire.