President Trump directed the Attorney General to draft regulations banning bump stocks after the October 21, 2017 shooting at the Route 91 Harvest Music Festival in Las Vegas, Nevada during which Stephen Paddock used AR type rifles with bump stocks installed on them to kill 58 people and injure approximately 500.  Bump stocks are replacement stocks that allow semi-automatic rifles to fire more rapidly by allowing the rifle to slide back and forth using the recoil energy so that the trigger is automatically pulled by the shooter’s stationary finger.

The ATF had previously examined the same type of bump stock devices and concluded that they were legal component parts for firearms that did not convert a semi-automatic rifle into a machinegun, and were therefore not regulated by either the Gun Control Act or the National Firearms Act.  After the October 21, 2017 shooting, the ATF concluded that its prior determination that bump stocks are legal “did not include extensive legal analysis of the statutory terms “automatically” or “single function of the trigger,” and reversed its earlier decision.

On December 26, 2018, the ATF published in the Federal Register revisions to three provisions in the Code of Federal Regulations defining the term “machine gun,” to clarify that bump stocks are covered by the definition of a machine gun.  The information published in the Federal Register can be found at  The changes go into effect on March 26, 2019.  The new revisions state that for purposes of the prior definition of a “machine gun”:

the term “automatically” as it modifies “shoots, is designed to shoot, or can be readily restored to shoot,” means functioning as the result of a self-acting or self-regulating mechanism that allows the firing of multiple rounds through a single function of the trigger; and “single function of the trigger” means a single pull of the trigger and analogous motions. The term “machine gun” includes a bump-stock-type device, i.e., a device that allows a semi-automatic firearm to shoot more than one shot with a single pull of the trigger by harnessing the recoil energy of the semiautomatic firearm to which it is affixed so that the trigger resets and continues firing without additional physical manipulation of the trigger by the shooter.

Accordingly, when the new regulations go into effect on March 26, 2019, bump stocks will be considered machine guns.  It has been illegal to register new machine guns for legal ownership by civilians since May 19, 1986, so possession of bump stocks will be illegal and persons who own they cannot legally continue to possess them when the new regulations go into effect.  Bump stocks must therefore either be destroyed, or surrendered to the ATF, on or before March 26, 2019.

Gun Owners of America filed a lawsuit in the U.S. District Court for the Western District of Michigan on December 26, 2018, challenging the new bump stock rule on the basis that it exceeded the ATF’s authority because the statutory definition of a “machine gun” was not changed and the ATF simply changed its prior interpretation of that term because of political pressure.  This lawsuit could potentially effect the terms of the new regulations banning bump stocks, or the effective date of those regulations.