Why The Gun Lobby Is Terrified Of California - from Mother Jones - *5-cent tax on each bullet*

[AtheistCrusader]

151. Well, from Heller

"We must also address the District’s requirement (as applied to respondent’s handgun) that firearms in the home be rendered and kept inoperable at all times. This makes it impossible for citizens to use them for the core lawful purpose of self-defense and is hence unconstitutional."

Removing access to ammo would do precisely that.
A tax is clearly permissible (11% already applied at the federal level for rifle ammo).
Any tax applied would have to meet some bar of reasonableness, which is hard to define, as there are few precedents. Could a 5 cent tax be applied per round and survive? That would make a box of Winchester Xpert .22lr cost twice as much. I doubt that would survive. Maybe if you exempted rimfire ammo, and only taxed centerfire at that rate, you might come up with something that would pass muster.