How can I own an assault rifle?

I want to own an assault rifle. Object to this if you must, but I am starting to become jealous because I see all of this people on YouTube holding ak47s, m16s etc, and firing them in full auto. I want to own a kind of gun like that but I live in Australia and I have to move to USA to own one. So how can I own an assault rifle without having to move to America because I heard that their economy is rock bottom right now.