ALLENTOWN, Pa. — In an instructional video shared with local law enforcement, a firearms expert empties a 30-round clip in about 12 seconds.
A moment later, he adds a small device to the same gun — a piece of steel about the size of his thumb. Once it's in place, he fires 29 rounds in about two seconds. It would have been all 30, but the gun jammed after the first shot.
The small insert is commonly known as a Glock switch, though they're not made by the Austrian firearms company. The Bureau of Alcohol, Tobacco and Firearms refers to them as machine gun conversion devices or MCDs.
Whatever you call them, they transform a legal semi-automatic pistol into an illegal, fully automatic weapon. With one squeeze of the trigger, the user can empty their weapon.
"These are significantly more dangerous than any other weapon law enforcement comes in contact with," said Lehigh County District Attorney Gavin Holihan. "Automatic weapons are extremely rare to run into. These Glock switches are small. They're easy to obtain, and they're cheap."
Becoming more common
Holihan, a Republican serving his first year in office, released the video as part of a larger educational presentation. The small devices are so easy to overlook and so new that local police were unknowingly turning in modified firearms as part of other investigations.
While he has no hard data, he said the anecdotal evidence is piling up that MCDs are becoming more common across the region. Witnesses who report shootings are increasingly describing the sounds of machine guns. Investigators are finding dozens of shell casings at some crime scenes.
"I don't think there's any reasonable person who says, 'That's what we need.' Sportsmen don't use it. Hunters don't use it. Law enforcement is endangered by it."Lehigh County District Attorney Gavin Holihan on machine gun conversion devices
And in at least two homicides in the last three years, evidence suggests an automatic weapon was used; Holihan declined to say which ones as they are part of ongoing investigations.
"I can tell they're becoming more common because there used to be zero (cases) but now there are some," Holihan said.
Federal authorities say it's not just a local phenomenon. Police departments nationwide reported a 570% increase in MCDs between 2017 and 2021, according to the ATF.
That roughly coincides with the advent of 3D printing, allowing people to quickly and cheaply construct their own MCDs without any direct know-how in welding or manufacturing. Under federal law, the devices are considered a machine gun even when they're not attached to a firearm.
“A pistol with an illegal MCD is dangerous. They are very difficult to control and fire a large number of bullets with one trigger pull. The risk of bystanders being shot is high when these are used," said Eric J. DeGree, the special agent in charge for the ATF Philadelphia Field Division.
The trend has alarmed Northampton County District Attorney Stephen Baratta enough that his office has invited the ATF to make a presentation on the devices to his prosecutors next month.
Baratta has said he's not aware of any current investigations in Northampton County where the devices have been used, but it's likely just a matter of time, he said.
"We are aware of it, and it will be, obviously, a problem once they get to be popular here," Baratta said
Pa. lawmakers pass on their own ban
Former President Donald Trump's administration banned MCDs in 2018 in response to the deadliest mass shooting in American history. In 2017, a single gunman killed 60 people and wounded more than 400 others when he opened fire at a Las Vegas music festival from a sniper's perch with rifles modified with bump stocks — another device capable of converting semi-automatic weapons into automatic ones.
But the U.S. Supreme Court is hearing a case testing the legality of that rule. The George W. Bush and Barack Obama administrations considered the devices legal, and a Texas gun shop owner has sued to have that interpretation reinstated. The Biden administration is defending the rule, arguing it matches the intent of laws passed in the 1930s that severely limited access to automatic weapons.
The Pennsylvania House voted against banning the devices last month by a 101-100 vote. One Democrat, state Rep. Frank Burns, D-Cambria, joined every Republican in voting down the bill; 102 votes were needed to pass the legislation.
The bill's narrow failure frustrated state Rep. Josh Siegel, D-Lehigh. For about 30 years, state and federal government has largely refused to act in the face of rising gun violence, he said. Banning MCDs and similar devices like bump stocks, he said, should have been an easy bipartisan step to protect the public and law enforcement.
Instead, he said, it seems Republican lawmakers are afraid to step out of line with the powerful gun lobby.
"This is what should be a common sense, no argument solution — make it illegal to have them, make it easier to prosecute them," Siegel said.
Republican state Reps. Milou Mackenzie, Ryan Mackenzie and Zach Mako, all who represent parts of Lehigh County, did not return phone calls and media inquiries about their votes on the bill.
'Law enforcement is endangered by it'
Holihan expressed disappointment that the House didn't pass a state ban, saying the most generous explanation was that lawmakers were unaware of the dangers MCDs posed.
But that doesn't alleviate the threats they present the public and police, he said, or allow local prosecutors to charge people in possession of them.
"I don't think there's any reasonable person who says, 'That's what we need,'" Holihan said. "Sportsmen don't use it. Hunters don't use it. Law enforcement is endangered by it."
