"To legally own a machine gun, you first have to apply for approval from the federal government. After purchasing the gun, you must fill out an ATF Form 4 application and wait for approval before taking possession of the firearm. The FBI conducts a thorough background check using fingerprints and a photograph required with your application, which could take 9 to 12 months to process. The gun will need to stay in possession of the previous owner until the process is complete.
In addition, you will need to pay a $200 “NFA tax stamp” for each weapon transaction. If approved, you will receive your paperwork in the mail, including a permit with the listed lawful possessor of the firearm. Only then can you take the machine gun home and possess it legally."