US President Donald Trump has signed an order to outlaw "bump-stock" devices for guns.
It's his first step during his administration towards tightening fire arms regulations. He has also said he may consider other restrictions after last week's school shooting in Florida.
The device enables a rifle to shoot hundreds of rounds a minute, turning a legal semi-automatic rifle into a machine gun.
They can be bought without the need for a criminal background check.
It puts Trump at odds with the powerful National Rifle Association that has previously opposed efforts to ban them.
The move would bypass Congress, where legislation to ban "bump stocks" has failed since an October massacre in Las Vegas.
The device then was used by a shooter who killed 58 people at an outdoor country music festival.