So, the state laws are useless in this case, essentially,
Yup, here's another example.
Under TX law ""Machine gun" means any firearm that is capable of shooting more than two shots automatically, without manual reloading, by a single function of the trigger."
It would be legal under TX state law for me to build myself a firearm that fired only two shots each time I pulled the trigger. But I would still be liable to prosecution under federal law because they also have jurisdiction and the applicable federal law is more restrictive.