Possessing “Glock switches’’ that turn a normal pistol into a de facto machine gun would be illegal under the sweeping gun bill the state Legislature passed last week, potentially closing what advocates called a loophole that had fueled increasing automatic gunfire on city streets.
The change was pushed by police and prosecutors who say they have seen a spike in the use of automatic weapons. State law, as the Globe reported in December, had allowed people to have the devices as long as they are not affixed to a gun.
Governor Maura Healey signed the new measure into law Thursday. Possession of the conversion device could carry a sentence up to life behind bars — the same penalty as having a machine gun without a license.
The bill tightens the state’s already strict firearm laws. The laws include regulating assembled “ghost guns’’ and strengthening “red flag’’ laws that allow the courts to remove people’s firearms.
In the end, there was broad support for criminalizing possession of the conversion devices, said state Representative Michael Day. Members of his conference committee that negotiated the bill saw the switches as having little value besides as a tool of street violence.
“The only thing they do is turn an otherwise legal firearm into an automatic weapon,’’ the Stoneham Democrat said.
Day said the law involves a “holistic’’ approach to gun control, seeking to ban any “automatic parts’’ that cause a gun to fire multiple bullets with one pull of a trigger. That, he said, should allow law enforcement to adapt to future modifications so the law doesn’t fall behind new technology.
The switches, also known as converters or chips, can be easily created by anyone with a 3-D printer, such as the pair whom federal authorities charged last year with manufacturing and selling them out of a Roxbury home. The implements are small chunks of plastic that can toggle a gun between firing one bullet or multiple ones with each trigger pull. When in fully automatic mode, a weapon can fire up to 1,200 rounds per minute, federal authorities said.
The devices have been linked to a wave of violent incidents. In Boston last year, a 15-year-old girl was one of five people wounded by a gun using a switch; in Springfield, police said the switches appear linked to the 70 percent increase in the number of shell casings recovered at shooting scenes last year.
Adding to the concern is the fact that the devices can be created with a $200 printer and downloadable instructions readily available over the internet. The conversion devices are also sold on e-commerce websites and shipped from China, frequently advertised as key chains or wall hooks to avoid detection, authorities have said.
They generally work on handguns manufactured by Glock and “ghost guns’’ assembled from kits purchased online or using 3-D-printed components, federal authorities told the Globe last year.
Possession of a switch was already illegal under federal law whether the item is attached to a gun or not, but local prosecutors have taken issue with how the switches are only illegal under state law when attached to a gun.
Suffolk District Attorney Kevin Hayden praised the measure. He said law enforcement in Boston continues to find unaffixed switches for which it is unable to bring charges, though it does refer some to federal authorities, who can choose whether or not to take up the case.
“With this measure the Legislature is proving once again that Massachusetts is a national leader in creating smart, common-sense laws to address the societal threat of illegal firearms,’’ Hayden said in a statement. “Enabling law enforcement to prosecute those using, possessing, and selling these devices is a major step forward.’’
Other cities have also been plagued by the proliferation of switches, particularly in the South. But more recently, authorities said, they began showing up in increasing numbers in Boston, Springfield, and other urban areas across the state.
State Senator John Velis, a Westfield Democrat, said, “These dangerous devices exist for no reason other than to cause destruction. Whether they are attached to a weapon or not they need to be taken off the streets and I am happy we have finally provided a way for local and state law enforcement to do so.’’
Sean Cotter can be reached at sean.cotter@globe.com. Follow him @cotterreporter.
