1. Congress has the power to tax (Article I, Section 8, Clause 1 US Constitution)
2. All States have the power to tax (innumerable state Constitutions)
3. All Rights "can be" regulated. (Supreme Court increasingly ad nauseum)
4. Taxes are one means of "regulating" (US history forever ad nauseum)
5. The 2A is a "Right"
6. All 2A Rights can be taxed.
7. (not to be forgotten...) The power to tax is the power to destroy. See again McCulloch v. Maryland, 17 U.S. 316 (1819) op cit
8. Any "rights" assumed under 2A can be effectively destroyed without ever directly addressing the central issue.