The ban on bump stocks approved by the city council in January was considered largely symbolic. Denver had previously banned the types of semi-automatic rifles that can be modified with bump stocks.
A bump stock is a device that can increase the speed in which a gun can be fired.
The council also made it illegal in most situations to possess magazines that hold more than 15 rounds of ammunition.
Fines under the new Denver law could be as much as $1,000 and up to 180 days in jail.