I noticed someone claiming that automatic weapons are banned in the United States of America. This is probably true in a few states, though not in the sense that it would be in other countries. They would be illegal to transfer within the state, without theft of lawfully held property having taken place.
In the US, we have our automatic weapons taxed a flat rate of $200 by the federal government at the time of transfer. It happens that the ones that are legally held, to my knowledge, are virtually never used in crime. A sizeable amount are not registered, not out of dishonesty but because the owner anticipated action like that seen in places where property rights are not respected, or because they persistently believe a particular measure isn't valid law. This is not an endorsement of ignoring ATF protocol. Right or wrong, they will most likely get away with violating your rights and charge you with a felony.
Most people acquired their property prior to 1986 when the federal government started strictly controlling new production. Still, there are places where new weapons having been extralegally built/converted are encountered by police officers often enough because they were carried by criminals. It is presently legal for civilians to procure new "machine guns" if they are well enough connected to something the government takes interest in. It is expensive, but also legal in most states if they obtain proper licensing with the federal government for manufacturing.
In most states, automatic weapons are not banned. It would be pointless.