Rocket Stove ping.
Take a look at this:
Ammo Can Rocket Stove
http://www.bearridgetradingpost.com/2011/07/ammo-can-rocket-stove/
I built one it and it wasn’t hard at all.
Here is a thread on it:
http://www.freerepublic.com/focus/f-bloggers/2850938/posts