In New Mexico, police and prosecutors backed an effort to outlaw devices that convert pistols into machine guns. In Alabama, the governor made it a priority.

Lawmakers in both states — one led by Democrats, the other by Republicans — responded this year with new laws making so-called Glock switches illegal.

At least half of U.S. states now have similar laws prohibiting the possession of such devices, a list that has grown over the past decade as law enforcement officers have found more of the tiny yet powerful devices attached to guns.

States are mimicking federal law, which for for decades has generally prohibited machine guns and any parts that can transform semiautomatic weapons into automatic ones.

What does federal law say?

U.S. law defines a machine gun as a weapon that automatically fires more than one shot with a single pull of a trigger. The definition also includes any parts designed to convert a weapon into a machine gun.

Federal law prohibits possessing machine guns made after 1986, with some exceptions for law enforcement, the military and certain licensed dealers. Nearly all conversion devices are illegal because they were made more recently.

People convicted of possessing machine guns and conversion devices can face up to 10 years in prison.

What is a Glock switch?

A Glock switch is one type of a machine gun conversion device. It’s a metal or plastic piece, about the size of a coin, that attaches to the back of Glock pistol, a brand that is popular with both police and criminals. The switch interferes with a gun’s internal trigger components so that it fires continuously when the trigger is pulled back and held.

A gun outfitted with a switch can fire dozens of bullets in mere seconds, similar to a factory-made machine gun.

Other brands of pistols that mimic Glocks also can be converted to machine guns. So can some semiautomatic rifles. Such conversion devices also are referred to as auto sears, selector switches or chips.

What does the data indicate?

The use of auto sears spiked in the past decade, partly because they can be made inexpensively with 3D printers.

From 2012 to 2016, just 814 machine gun conversion parts were taken into custody by the Bureau of Alcohol, Tobacco, Firearms and Explosives. That swelled to 5,454 from 2017-2021.

In January, former President Joe Biden’s administration said 12,360 suspected machine gun conversion devices had been recovered in the U.S. and submitted to the ATF during a roughly 34-month period ending in October 2024.

Five states including Florida, Illinois, Texas, Montana and North Dakota accounted for nearly half that total.

What have states been doing?

Alabama is the latest state to outlaw Glock switches. A law signed this month by Republican Gov. Kay Ivey makes possessing parts designed to convert pistols into machine guns a felony punishable by up to 10 years in prison.

The bipartisan push in Alabama came after police said they believed conversion devices had been used in fatal shootings, including one in September that killed four and injured 17 people outside a Birmingham lounge.

Democratic New Mexico Gov. Michelle Lujan Grisham signed a law in February making possession of a weapon conversion device a felony punishable by up to three years in prison.

Similar legislation passed the New Jersey General Assembly last week and now heads to the Senate. Bills also are pending in other states.

Republican Virginia Gov. Glenn Youngkin signed a law last year making auto sears illegal. But Youngkin vetoed legislation this past week that would have broadened an existing ban on “trigger activators” to cover additional devices that increase firing rates of semiautomatic weapons.

What do gun control advocates want?

Groups such as Everytown for Gun Safety say state laws provide a sometimes easier alternative to federal prosecution for possessing Glock switches. But they want to go further.

Everytown for Gun Safety is backing legislation in California, Maryland and New York that would make it illegal to sell pistols that could be transformed into machine guns.

“That really puts the pressure where it belongs — on the manufactures that are making money off of guns that they know can be readily turned into machine guns,” said Nick Suplina, senior vice president for law and policy at Everytown for Gun Safety.

Several cities and states including Baltimore, Chicago, Minnesota and New Jersey have sued Glock for making pistols that can be converted by others to automatic weapons.

What do gun-rights groups say?

The National Rifle Association notes U.S. attorneys already can prosecute people for misusing gun conversion devices without the need for state laws.

Gun Owners of America, another gun-rights group, contends people should have a Second Amendment right to own machine guns. State laws against machine gun conversation devices are “duplicative” and “pure virtue signaling,” said Aidan Johnston, federal affairs director for Gun Owners of America.

He said guns converted to fire automatically can have practical uses like eliminating large groups of feral hogs that are destroying land.

“Just because you put that on your firearm doesn’t mean that you are a violent criminal or that you necessarily are a dangerous person,” Johnston said.