In March, eight Philadelphia high school students waiting for a city bus were mowed down by rapid gunfire. Last October, a police officer in an airport parking garage confronted a thief breaking into a car, only to be killed by a similar burst of gunfire.

Philadelphia Police believe that the gunmen in both of these cases augmented their weapons with Glock switches. Even as the number of fatal and nonfatal shootings across the city declines, rate-of-fire acceleration devices, like bump stocks and Glock switches are wreaking havoc on the streets of Philadelphia, officials say. Bump stocks make semiautomatic rifles fire more like machine guns by enabling an increased rate of fire. Switches function similarly on handguns.

In response, just days after the U.S. Supreme Court struck down a Trump-era federal prohibition on bump stocks, Mayor Cherelle Parker made Philadelphia the latest city to ban the devices. On June 18, she signed a bill forbidding the sale, purchase, possession, and manufacture of bump stocks and other rate-of-fire acceleration devices. With “devices floating around Philadelphia like these so-called switch devices which can turn a handgun into a machine gun, there is no time to rest and or slow down,” Parker said at the bill-signing ceremony at City Hall.

With Parker’s signature, Philadelphia joined 16 states and a handful of cities, including Washington, D.C., and Boulder, Colorado, in banning bump stocks. Her decision, though, could have limited effect. A state law specifically forbids local governments from restricting firearms, and because of questions about the degree to which that law extends to accessories for guns, it’s hard to say what, exactly, the ban will mean in Philadelphia. 

It’s already proving to be controversial. Just days after the bill signing, lawyers representing two local gun owners sued the city in federal court. “Pennsylvania law is crystal clear, Philadelphia is not permitted to regulate firearms in any way,” said attorney Andrew Austin, who represents plaintiffs Ross Gilson and Vern Lei.

Parker’s spokesperson said the city will “energetically” defend the law in court. “We’ll leave no stone unturned to keep Philadelphia safe,” Joe Grace said.

Philly officials say the law will fill a gap left by the invalidated federal ban. It is being embraced by the city’s Police Department, which has struggled to hire officers and close shooting cases with arrests in recent years. “Because this was not illegal at all in the state or local – it was only a federal crime – we need some kind of deterrent here,” Deputy Police Commissioner Frank Vanore said.

Bump stocks work by harnessing a firearm’s recoil energy to quickly re-engage the trigger as long as the shooter maintains pressure. With the device, a semiautomatic rifle can function more like a machine gun. In 2017, a Las Vegas gunman used firearms equipped with bump stocks to kill 60 people and injure hundreds more at a country music festival. A year later, the federal Bureau of Alcohol, Tobacco, Firearms and Explosives issued a ruling redefining bump stocks as machine guns, which are illegal, thus banning them at the federal level. On June 14, the nation’s highest court struck down that ban, ruling that the government had exceeded its authority by imposing it.

While the court’s ruling does not extend to state and local restrictions, Philadelphia’s new law may draw more legal challenges at the state level. Under Pennsylvania law, counties, townships, and municipal governments are barred from regulating “the lawful ownership, possession, transfer or transportation of firearms, ammunition or ammunition components when carried or transported for purposes not prohibited by the laws of this Commonwealth.” Similar so-called preemption laws exist in multiple states. 

In May, Pennsylvania’s Democratic-controlled House of Representatives narrowly failed to adopt two gun-control bills: a ban on bump stocks and similar devices, and a bill that would have required gun sales records to be filed electronically. Backers of the bump stock law in Philadelphia are more optimistic about its success and believe it will withstand legal challenges. They point to a February state appeals court ruling that upheld the city’s 2021 ban on ghost guns, finding that the ban was on the manufacturing of gun parts and not guns.

Philadelphia City Councilmember Curtis Jones, who introduced the legislation, noted that in addition to that decision, Polymer80, the nation’s largest ghost gun manufacturer, recently paid the city $1.5 million as part of an out-of-court settlement.  

“This is not against guns,” Jones said. “It is against the use and manufacturing of apparatuses that enhance the velocity of trigger pull.” He said the lawyers who will represent the city in court believe that distinction “puts us on solid ground to say that this apparatus is not necessary to protect the rights of legal gun owners.”

Similarly, Adam Garber, executive director of CeaseFirePA, said his gun violence prevention group believes the law will be upheld. “We believe this will save lives because as the courts have upheld the ghost gun ban, the city has the complete authority to regulate parts of firearms and not firearms themselves,” he said. 

Jones said that Parker herself asked him to introduce the bill. “Mayor Parker, the boss lady, basically said, ‘Enough is enough,’” he recalled. “We’re trending in the right direction but not quick enough. For the victims of gun violence, the fact that we are down close to 40 percent from last year is not a comforting fact. We have to keep moving.”