They already have something like this in California- you have to have a weapon in the correct caliber before you can buy the ammunition. And every ammo sale requires a NICS check, IIRC.
But, this is nothing new; antis have been suggesting onerous ammo taxes, for example. They know if they cannot get the weapons, then making ammo unavailable is their next best bet.
It is also interesting how many people who had no interest in guns are now running to gun stores once things got real. Reminds me of the old joke: "What's the definition of a neo-conservative? A liberal who just got mugged."
