Caison Robinson, 14, had just met up with a younger neighbor on their quiet street after finishing his chores when a gunman in a white car rolled up and fired a torrent of bullets in an instant.

“Mom, I’ve been shot!” he recalled crying, as his mother bolted barefoot out of their house in northwest Las Vegas. “I didn’t think I was going to make it, for how much blood was under me,” Caison said.

The Las Vegas police say the shooting in May was carried out with a pistol rigged with a small and illegal device known as a switch. Switches can transform semiautomatic handguns, which typically require a trigger pull for each shot, into fully automatic machine guns that fire dozens of bullets with one tug.

By the time the assailant in Las Vegas sped away, Caison, a soft-spoken teenager who loves video games, lay on the pavement with five gunshot wounds. His friend, a 12-year-old girl, was struck once in the leg.

These makeshift machine guns — able to inflict indiscriminate carnage in seconds — are helping fuel the national epidemic of gun violence, making shootings increasingly lethal, creating added risks for bystanders and leaving survivors more grievously wounded, according to law enforcement authorities and medical workers.

The growing use of switches, which are also known as auto sears, is evident in real-time audio tracking of gunshots around the country, data shows. Audio sensors monitored by a public safety technology company, Sound Thinking, recorded 75,544 rounds of suspected automatic gunfire in 2022 in portions of 127 cities covered by its microphones, according to data compiled at the request of The New York Times. That was a 49 percent increase from the year before.

“This is almost like the gun version of the fentanyl crisis,” Mayor Quinton Lucas of Kansas City, Mo., said in an interview.

Mr. Lucas, a Democrat, said he believes that the rising popularity of switches, especially among young people, is a major reason fewer gun violence victims are surviving in his city.

Homicides in Kansas City are approaching record highs this year, even as the number of nonfatal shootings in the city has decreased.

Switches come in various forms, but most are small Lego-like plastic blocks, about an inch square, that can be easily manufactured on a 3-D printer and go for around $200.

Law enforcement officials say the devices are turning up with greater frequency at crime scenes, often wielded by teens who have come to see them as a status symbol that provides a competitive advantage. The proliferation of switches also has coincided with broader accessibility of so-called ghost guns, untraceable firearms that can be made with components purchased online or made with 3-D printers.

“The gang wars and street fighting that used to be with knives, and then pistols, is now to a great extent being waged with automatic weapons,” said Andrew M. Luger, the U.S. attorney for Minnesota.

Switches have become a major priority for federal law enforcement officials. But investigators say they face formidable obstacles, including the sheer number in circulation and the ease with which they can be produced and installed at home, using readily available instruction videos on the internet. Many are sold and owned by people younger than 18, who generally face more lenient treatment in the courts.

Social media platforms like YouTube ban content that shows people how to make illegal weapons. However, such content is protected under the First Amendment and remains widely available online.

Federal law enforcement officials have contacted Glock, the company that produces a weapon that has come to define an entire class of easily available 9 millimeter handguns, in search of ways to modify the weapon to make it harder to attach switches. Carlos Guevara, a vice president at Glock, said the company has collaborated with law enforcement officials to target illegal sellers and users of switches but has determined the design of the pistol cannot be altered in that way.

In 2021, a man with a gun modified with a switch fired at two police officers in Houston, killing one and injuring the other. One of the gunmen in a 2022 gang shootout in Sacramento that left six dead and injured 12 people carried a gun fitted with a switch, according to the police. In recent months, shootings using modified weapons have been caught on camera in Milwaukee, prompting the city’s mayor to compare the scene to a war zone.

Dr. James Miner, the chair of emergency medicine at Hennepin Healthcare in Minneapolis, which has the largest trauma center in Minnesota, said he first heard about switches in 2020 when he was trying to make sense of why gunshot victims were arriving at the hospital with numerous wounds and why more people seemed to be reporting being shot by stray bullets.

 

Physicians at Hennepin County Medical Center say they have seen an increase in the number of wounds shooting victims have as switches have become more common.Credit…Jenn Ackerman for The New York Times

“It’s more common now for someone to say: ‘I was walking down the street and I heard the sound and all of a sudden my leg hurt, my chest hurt,’” he said. “Rather than: ‘I was held up or I was involved in a drug deal gone wrong.’”

Since the 1930s, federal laws have tightly restricted ownership of machine guns outside of the military and police departments. In 1986, Congress banned the production of new machine guns for civilian use, making them even more uncommon in the years that followed.

Devices to turn firearms fully automatic have existed for years, but they had not been a major concern for the authorities until recently.

In 2019, federal agents began seizing a significant number of switches imported from China, said Thomas Chittum, a former associate deputy director at the Bureau of Alcohol, Tobacco, Firearms and Explosives who now oversees analytics and forensic services at Sound Thinking.

Soon, the authorities began seeing a rise in switches — which in 2019 sold for as little as $19 — in several major American cities. Between 2017 and 2021, the A.T.F. recovered 5,454 machine gun conversion parts, a 570 percent increase from the preceding five years.

Steven M. Dettelbach, director of the A.T.F., said that trend ominously echoed the days of “Al Capone and the Tommy gun,” when criminals often had more firepower than law enforcement.

In an interview, he recalled having asked one of his advisers to bring an inexpensive 3-D printer to his office last year to show how a switch was made. The speed, ease and cheap cost, he said, were chilling.

He said they handed one to him “after a half-hour, 40 minutes.”

The Justice Department has stepped up prosecutions of sellers and suppliers over the past few years. Under the Gun Control Act of 1968, it is a crime to manufacture a machine gun, a violation that carries a maximum of 10 years in prison. Last week, prosecutors in Chicago charged a 20-year-old man with selling 25 switches and a 3-D printer to an undercover agent. In November, federal prosecutors in Texas charged a supplier who, they assert, had sold thousands of switches — shipping some inside of children’s toys.

A shooting target after a demonstration of a switch at a training facility in Minnesota.Credit…Jenn Ackerman for The New York Times

Switches are fast becoming embedded in youth culture, and have been the subject of rap songs and memes on social media. One of four teenagers accused in the killing of an off-duty Chicago police officer this year posted on the internet a song called “Switches,” rapping “shoot the switches, they so fast” as he showed an arsenal of weapons.

Caison Robinson said he knew about switches before he was nearly killed by one. Teenagers he knew began bragging about having acquired the converted guns, often from older siblings, he said. They called the switches “buttons,” he said, which came in several colors.

“It’s become a thing you get to be cool,” said Caison, who said in an interview that he tried to steer clear of armed cliques of teenagers in his Las Vegas neighborhood. “It’s like a trend now.”

His mother, Takeila Peebles, moved to Las Vegas from Chicago seven years ago. She said she thought he would be safer in their new city.

The day of the shooting, Ms. Peebles, who works in medical billing and as a chef from her home, told Caison he could go outside to play only after he tidied up his bedroom, threw in a load of laundry and vacuumed the stairs. When Caison finished his chores, around 3:45 p.m., he headed out. Not long after, she heard gunfire and caught a glimpse of a white Kia Optima speeding away.

A soldier in uniform who happened to be nearby saw what had happened and tended to Caison’s wounds until a passing motorist rushed him to the hospital.

One bullet struck his colon, part of which had to be removed, medical officials say. Another pierced his liver. A third punched through a principal vein in his abdomen. The other bullets broke his femur and caused nerve damage to his forearm.

Investigators concluded that the shooting was tied to a gang dispute and that Caison was not the intended target. In late June, Hakeem Collette, 17, pleaded guilty to battery with a deadly weapon and was sentenced to 10 years in prison. He will be eligible for parole in two years.

Caison’s mother, Ms. Peebles, said the punishment is outrageous, considering the anguish her family has experienced. For three weeks after her son was shot, she had a recurring nightmare in which she watched helplessly as Caison bled to death on the pavement.

Lately, Ms. Peebles said she often tiptoes into his bedroom to make sure he is still there.

“I’m always at a loss for words when I look at him,” she said. “He’s not a touchy person, but I just always want to hug him.”