The NFA is a tax and has been upheld under Congresses taxing authority. When the tax became zero and no revenue was collected, a Federal Court ruled that Congress had no authority to run the registration and prior approval apparatus that was used to prove tax compliance. Lot's of complicated stuff about injunctions applying only to plaintiffs and orgs, but the DOJ did not appeal, and now the ATF has said they are making this uniform. This does not change state laws that under State statute make it a crime to have such items or to have such items that are not registered.

I am not a lawyer, but I am generally interested in firearms and firearms law.

A reasonably good source is Mark Smith on YouTube. He is an attorney.

Hope this helps.