This is a good article from the Christian Science Monitor: http://www.csmonitor.com/USA/Politics/2016/0623/Why-Australia-isn-t-a-model-for-US-gun-control

This particular paragraph, I find significant because it is something that I have been saying but find it rarely in print.

"The sheer number of firearms in America today – an estimated 300 million – would also present practical and financial obstacles. If the US were to collect and destroy the same proportion of firearms as Australia did, it would require a buyback of 90 million weapons, according to one Australian researcher, as compared to only 640,000 firearms bought back by the Australian government. Paying full market value for the guns could cost the US billions of dollars. "