If the claim has any legitimacy at all, it would have to be derived from Article X, which states: "The powers not delegated to the United States by the Constitution, nor prohibited by it to the states, are reserved to the states respectively, or to the people. "
In other words, he's saying that just because the Federal Government doesn't have the power to ban private firearms, because this proscription only applies to the Fed, and since it is "not delegated to the United States by the Constitution, nor prohibited by it to the states", it is reserved for the states to decide. This approach only assumes that the states have reserved this power, and completely ignores the phrase "or to the people".
I'm not a lawyer, nor do I pretend to be one in bars in order to pick up women, but IMHO it's a pretty damn flimsy pretext. It's kind of like saying that none of the Bill of Rights or subsequent amendments apply to the state governments, and I can't remember the case, but there was a Supreme Court ruling that the Federal Laws trump the state laws if there is a conflict.
The liberals are fine with that in first amendment situations, but they seem to want to exlude the Second, for some reason...
AH but it IS "prohibited by it to the states" right here:
"A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed."