It won't really shut down manufacturing. The current supply is already very high, and will last a long time. On top of that, 3-D printing/milling will be able to take over. The people who own lots of guns will be able to sell some and make a shit ton of money, and others will go into business making their own. Instead of a couple dozen gun manufacturers, you will have thousands, most of whom have a disdain for the government, and won't help them out in any fashion.
Prohibition does not work.