So, this attracts the ire of the state department. Yet, something like this (http://aresarmor.com/store/Item/TACMHL15) is actually approved by the ATF as not being a firearm. You just need some basic machining skills (thanks MIT OpenCourseWare) and access to basic tools (thanks local hackerspace) to have a fully operational AR-15 which does not need to be registered.
Seriously?