This article was very good about Australia and how they were able to confiscate guns and how something similar might look in the United States. The Australia "model" is popularly referenced by many folks as a result of recent shootings including the President.
I don't link many articles requiring the reader to click but this one is worth reading from the source:
http://thefederalist.com/2015/06/25/the-australia-gun-control-fallacy/