It would likely never happen, but say the US did actually clamp down on gun control. Like Australia, let's assume they institute a buyback program. Some kind of program would be needed in order to A) gain support B) actually reduce the amount of guns so that a huge black market isn't instantly created. However, after thinking about it, I believe there would be way too many guns out there for them to ever realistically do this, it would be a logistical and financial nightmare.
Let's assume their are 300 million guns out there that the US would want to "buy back" and let's assume they ONLY get 200 million, so not to overestimate. For one thing... holy crap. 200 MILLION guns. I can't even fathom it, I wonder if that would fill the saddledome to the roof? maybe two saddledomes? If there if a math wiz out there, I would love to hear how many saddledomes it would take to hold all the USA's guns.
For two... the cost, wow, just wow. Assume a conservative price of $200 per gun average for all guns that they buy. Don't want to get to bogged up in this number, if it's higher so be it. I can't see how it would be lower though.
200,000,000 x $200 = $40,000,000,000
40 Billion dollars
This is a conservative estimate too I think.
So we have a 40-50 billion dollar expenditure and an amount of guns so large it literally can't be comprehended without complex mathematical formulas. I think it's safe to say that the US is going to be filled to the gills with guns for a very, very, long time. Best intentions of future generations be damned, that is a ####load of guns.