We were talking about federal laws and courts. I assume that in a short blog post I'm not expected to address the proliferation of overlapping jursidictional priorities and conflicts. But since you insist on taking the discussion where it wasn't going...
Fact is, majority of US states do permit machinegun ownership, so long as it complies with federal law; thus if federal law permits felons building machineguns (so long as it remains in-state), majority of states would not prohibit it. Now that the discussion has clarified that the remaining prohibitions would occur in a minority of more than four dozen states, and that the federal government would have at least had no say in the matter (as opposed to compulsive legalization in all encompassed jurisdictions), and that the discussion had not been addressing state laws (or if it did, it was that the applicable state ALLOWED the activity), that for most practical purposes the one-sentence summary of the horribly verbose & convoluted verdict in question and its consequences was sufficiently accurate?
(Pardon me. I'm getting increasingly irritated by exchanges that amount to: "X." "X? You're WRONG because you didn't address minor tangential issues Y, Z, P, D, and Q in comprehensive detail, all of which had little to do with the discussion at hand.")
This is false. The related case would have left machine-gun building a matter of State law. Pure-Federalism is not the only possible form of governance, and it's not the US Constitution's approved form.