This is true, however I find it highly unlikely they can ban any ammo. Make it prohibitively expensive, sure. Make it scarce (as it already is) sure. However banning any specific caliber or just ammo in general is pretty pointless. This goes back to the hunting supporters- .223 is a common hunting caliber, as is .308, so on and so forth. Not to mention there are already so many people with stockpiles, plus reloading supplies...
Even in the panic, even with supplies being eaten up by the government, I've bought .22LR, .223, and .308 all locally, all for reasonable (although a little higher) prices.