Short version: All those guns people own aren't going to just evaporate,

or be turned in.  And you try that Australian or British Model Obama was so fond of talking about, the results would be bad.

Very.

One disagreement:
...252,443,229 records voluntarily input into the system by private manufacturers and wholesalers, each representing a unique gun serial number. That system has only been operational since 2000. Do we really think 252 million of the “300 million” guns in the country passed through the hands of those individual dealers since 2000? Not likely. By his take, it’s quite possible that the total number of guns is vastly under reported, and the true number is between 329 million and 660 million, with a reasonable guess being 413 million firearms. He could be wrong, but I find his argument compelling.
Having seen the numbers some people have worked out, I strongly suspect the number is on the high end.  Or a bit more.  I know people who own firearms made in the mid-1800's that still work; take care of things, and they last a loooong time.  I've also known people who will NOT buy a gun at a store, because paperwork: they're honest people, no criminal record, so private sales(in America) are legal, and they figure it's none of the damned business of the .gov what they own.*



*I suspect that some immigrants from places where Holy Mother Socialism has been the rule tend to feel the same way; once they're citizens and can legally own arms, were I one of them, I'd try to keep it off the books, too.