Here's my favorite argument, never used as near as I can tell:
The Second Amendment to the Constitution is just that, an amendment. It is not simply another clause tacked on for good measure. The function of an amendment is to amend, to improve by change, the entire document to which it applies. The Bill of Rights changes each and every clause in the original Constitution that is inconsistent with any part of any of its amendments.
For example, 18 USC §930 depends on the Interstate Commerce clause. The original version lacked any authority, and was struck down as ultra vires. Congress added a statement of authority resting on the Interstate Commerce clause. The Court found that to be an adequate basis. What the Court did not consider is that the Bill of Rights amended the Interstate Commerce clause. So, in any case in which that clause be inconsistent with any part of the Bill of Rights, it cannot be used as authority for any statute. As if U.S. Con. Art. 1, § 8 said, "... To regulate commerce with foreign nations, and among the several states, and with the Indian Tribes; except where such regulation infringe upon the right of the people to keep and bear arms, practice their religion, print newspapers, etc."
On that basis, I submit that 18 USC §930 is unconstitutional, regardless of its reliance on the Interstate Commerce clause. Congress lacks the power to regulate firearms moving across state lines, much less in solely intrastate transactions on the theory that affecting interstate commerce is the same as engaging in interstate commerce. And, by the way, the holding in Wickard v. Filburn, 317 U.S. 111, which established that "principle", was that a man's failure to engage in interstate commerce constituted engaging in interstate commerce because his subsistence farming "affected" interstate commerce because he wasn't using any store-bought wheat. I find that whole theory totally absurd.