Free: Contests & Raffles.
Idiots......https://www.youtube.com/watch?feature=player_embedded&v=Y2sWiZ8BizI
That is a faked-up video. He swaps out two different lowers off camera. The airsoft one had a green handle, the finished one has a black handle, and if you look closely, the side of the receiver below the ejection port has some lettering stamped into it on the green handled one and it is not there on the black handled one. Also he doesn't put the bolt or mag releases back in that he removes, yet the finished gun has them in place and they work.
If you read the description of your video Smossy, you'll see the video was a joke. You cannot convert an airsoft into a working "military grade machine gun".