Since 1934 automatic weapons were required to be registered with the ATF, in 1986 they stopped registering new ones. You can still get pre 1986 automatic weapon

Since 1934 automatic weapons were required to be registered with the ATF, in 1986 they stopped registering new ones. You can still get pre 1986 automatic weapons, but you have to pay out the nose for them. I don't think a registered automatic weapon has ever been used in a crime.