<P> Most current fully automatic trigger groups will not fit their semi-automatic firearm look - alike counterparts--the semi-automatic version is specifically constructed to reject the fully automatic trigger group by adding metal in critical places . This addition is required by ATF to prevent easy conversion of Title I firearms into machine guns . </P> <P> For civilian possession, all machineguns must have been manufactured and registered with ATF prior to May 19, 1986 to be transferable between citizens . These machine gun prices have drastically escalated in value, especially items like registered sears and conversion - kits . Only a Class - II manufacturer (a FFL holder licensed to manufacture firearms or Type - 07 license that has paid a Special Occupational Tax Stamp or SOT) could manufacture machineguns after that date, and they can only be sold to government, law - enforcement, and military entities . Transfer can only be done to other SOT FFL - holders, and such FFL - holders must have a "demonstration letter" from a respective government agency to receive such machineguns . Falsification and / or misuse of the "demo - letter" process can and has resulted in long jail sentences and felony convictions for violators . </P> <P> Owning both a short barrel and a legal - length rifle could be construed as intent to build an illegal, unregistered SBR . This possibility was contested and won in the U.S. Supreme Court case of United States v. Thompson - Center Arms Company . ATF lost the case, and was unable to prove that possession of a short barrel for the specific pistol configuration of a Thompson Contender is illegal . ATF later released ruling 2011 - 4 to clarify the legal status of owning such conversion kits . </P> <P> Removal of a weapon from classification as an NFA firearm, such as the reclassification of the original Broomhandle Mauser with shoulder stock from "short barrel rifle" (SBR) to a curio or relic handgun, changed its status as a Title II NFA firearm but did not change its status as a Title I Gun Control Act firearm . </P>

When were machine guns banned in the united states