Do they work or do they exist? They work as well as new laws that don't change anything but take away due process will work.
What does the Second Amendment mean? And what gun control laws have been struck down by the courts? We already had a federal "assault weapon" and "large capacity magazine" ban. We won't have that again?
As for ammunition, California and Seattle and Illinois all tax it heavily. No court has overturned those laws on Second Amendment grounds. San Francisco makes you lock your gun in your safe or physically carry it on your body (meaning you can't have it ready to use unless it's in a holster on your jammies), and does not allow you to possess common hollow-point defensive ammunition. No court has overturned these laws. Many states ban so-called assault weapons and LCMs. Only the Fourth Circuit overturned such a Maryland law, and was quickly reversed en banc. Many states essentially ban carry outside the home, and only the DC Circuit has overturned such a law (so if you live in DC, maybe you can get a permit, but if you live in Prince George's County, tough shit forget it). The Supreme Court has not taken any of these meaningful cases.
People are not crazy to think that they should buy guns and ammo now if they want them when they are told that the government is coming and will outlaw the ammo, guns, and magazines everybody wants, or will tax them heavily, and the protection from the courts is scant, at best.