With the recent, tragic shootings perpetrated by sub-human individuals like those that took place Las Vegas and Orlando, there has been a great deal of discussion regarding the apparent availability of automatic weapons. While it appears that the Vegas shooting was done using modified semi-automatic weapons, I am writing only to address the restrictions in place upon true fully automatic machine guns.
Currently, the National Firearms Act (NFA) makes possession of fully automatic machine guns illegal under most circumstances. The only "legally transferable" machine guns the general public may possess are those manufactured and registered prior to May 19, 1986. A quick look at online sales websites such as gunbroker.com will show that these firearms are greatly expensive--often more than $15,000.
Not only does the expense of these firearms make them largely unattainable by most individuals, in order to purchase one, you must pass a thorough background check with the Bureau of Alcohol Tobacco Firearms and Explosives (BATFE). This process usually takes 9 months to a year. Only after passing the background check, paying the $200 tax stamp fee, and getting the chief local law enforcement officer to sign off on the sale, may you then receive the firearm.
Newly manufactured machine guns, which are much cheaper, can only be possessed by licensed gun dealers or manufacturers who have a Federal Firearms Class 3 license. Even these people with and FFL can only have a limited number of "dealer samples." That is because any machine gun manufactured after May 19, 1986 may only be sold to law enforcement or military---NO EXCEPTIONS.
While fully automatic weapons still exist in the public, they are very limited in number. Because of this limited number of transferable weapons, they are quite expensive, and most end up in the hands of collectors where they are kept under lock and key.
Whether or not the government should ban devices that enable a semi-automatic rifle, such as an AR-15, to operate more akin to a machine gun, i.e. the "Bump Stock", is a debate for another post. I merely wanted to help those who may be under the impression that you can walk into a local gun shop and purchase a fully automatic firearm understand that it just isn't so.