Since no one really told you about the installation here's my experience with it.
I did it the first time in about 15 minutes basically, just screwing in stuff, and all. I said basically because the Oring in the middle on the inside took me like an hour to get in. But after that, place your barrel inside the hop up(nub and bucking on of course.) screw in the set screws on the side that hold in your barrel, then put on that little silver ring thing(not sure of what it's called). Then you take the hop up and put it in through the part of the outer barrel with the threads that go into the receiver. Make sure to remember to put the spring on the arms. I made the mistake of forgetting... When I realized this, I had already assembled the rifle. But aside from that it's really simple. Everything you need is included.
I bought it from airsoft atlanta about 80 shipped.
This clown actually knows what he's talking about. He used to be really active in some other forum. He has 3 videos on this. Goodluck.