The 9th Circuit Court of Appeals (the one for CA, OR and WA, among other states) just handed down an opinion that says Congress' Commerce Clause authority does not extend to the power to ban home-made machine guns, because such guns are never in the stream of interstate commerce (NOTE: The decision has no effect on the power of states to ban such guns). This decision is consistent with an earlier 9th Circuit case that held Congress had no power to ban home-made, not-for-sale child porn under the Commerce Clause (but once again, states can ban it, via their reserved police power).
Remember folks, in our system of government, just because it's bad doesn't mean the federal government has the power to ban it. The federal government is supposed to be a government of limited, specifically delineated powers, whereas the states have general authority that is specifically limited in certain cases.
If you would like to read the decision, you can find it here:
Interestingly, this will likely have some ramifications to an earlier topic of discussion: drugs. It seems to me, and others, that home-grown marijuana or other home-produced drugs made for personal consumption would also thus be non-regulatable via the Commerce Power (which, for those who are rusty on their Constitutional Law, is the main power by which Congress passes its laws).
FYI, according to Larry Solum, professor of law at University of San Diego, there is a home-grown marijuana case pending before the 9th Circuit right now. I can't imagine that the Supreme Court would not take up these cases to weigh in again on the Commerce Clause, which they haven't done since they declared a Federal spousal abuse law was outside the Commerce Clause authority of Congress back in the late 90s.