Mexican authorities were outgunned by criminal cartels in two notable incidents this month. In both cases, the criminals were armed with high-powered .50-caliber firearms. First, on October 13, in the state of Michoacan, a police convoy was ambushed with .50-caliber sniper rifles, leaving 13 officers dead and nine wounded. Four days later, in the state of Sinaloa, the government was forced to abandon an operation to arrest the son of Joaquín “El Chapo” Guzmán, after his henchmen assaulted the authorities with both sniper rifles and truck-mounted machine guns.

“We are seeing a full-out criminal insurgency in Mexico right now,” said Robert Bunker, an international security expert who teaches at the Army War College Strategic Studies Institute and has written about the use of .50-caliber rifles by Mexican cartels.

Often, the weapons come from the United States, where civilian sales of high-caliber sniper rifles are unregulated in all but three states. The weapons are not legally sold to civilians in Mexico, but they end up in the country as a result of weapons trafficking or American arms exports to the Mexican government.

Data from the Mexican military, which tracks weapons recovered in enforcement actions, shows that hundreds of high-caliber weapons have turned up at crime scenes throughout the past decade.

The Mexican Army recovered 554 .50-caliber firearms from 2010 to 2018, according to data that activists obtained through public records requests to the Mexican Secretariat of National Defense (SEDENA). Of those, 496 were rifles, and 227 were made by Barrett, a Tennessee company that specializes in high-caliber sniper rifles. Of the remaining 105 weapons whose make could be identified — cartels frequently destroy the branding and serial numbers to disrupt tracing — all but one of the rest were made in America. About three-fifths of the weapons were recovered in the state of Tamaulipas, which borders south Texas, and at the major ports of entry at Laredo, McAllen, and Brownsville.

Compared to AR- and AK- style rifles, which are much more common both in the United States and Mexico, .50-caliber weapons shoot a much larger, faster, and thus more destructive projectile. The rifles are accurate over longer distances. Crucially, they can also be used against vehicles: A single bullet can pass all the way through a truck or split an engine block, and even disable a helicopter.

Experts say the use of .50-caliber weapons is part of an escalating arms race between cartels and the government. Members of Mexican special forces and police units, including in Sinaloa, are also equipped with American-made .50-caliber rifles. But this presents its own problems, since oversight of American firearm exports is poor and many Mexican public authorities are widely known to be corrupt.

“People begin to perceive that organized crime is more powerful than the state, and they have no place to turn. That creates a certain amount of despair,” said John Lindsay Poland, an anti-arms-trafficking activist who studies American weapons in Mexico and obtained the SEDENA data. “Some people in Mexican government say, ‘Let’s better arm the police or the army. Give them bigger caliber weapons.’ Then the criminal organizations respond in kind,” he said.

Despite the fact that .50-caliber rifles are freely available in 47 American states, the use of such weapons in the United States by mass shooters or other criminals is exceedingly rare, given their size and high price tag. A Barrett rifle retails for approximately $8,000. “Such prices are meaningless” to the cartels, however, said Bunker.

U.S. federal authorities have prosecuted a number of people for smuggling the high-powered weapons to Mexico in just the past two years. In September, an Arizona couple was sentenced to five years in prison after they pleaded guilty to smuggling three .50-caliber rifles and 16 AK-style rifles. This August, three Laredo, Texas, residents were arrested for lying on a background check form after they bought a .50-caliber rifle they were allegedly planning to smuggle to Mexico. Last October, a San Antonio man was arrested for his part in a conspiracy to smuggle weapons to Mexico after he sold a .50-caliber rifle to an undercover officer.

In perhaps the biggest .50-caliber smuggling case to date, a federally licensed gun dealer from Canfield, Ohio, was indicted in 2017 in connection with a scheme to supply 62 Barrett rifles to traffickers who resold the weapons in Mexico. The operation supplied cartels with more .50-caliber rifles than were captured by the Mexican Army in five of the nine years covered by the data that Poland provided to The Trace.

Davy Aguilera, a former agent of the Bureau of Alcohol, Tobacco, Firearms and Explosives who worked in Mexico as the drug war escalated during the 1990s and 2000s, was horrified by video of cartels firing on police with high-caliber weapons. “Those are weapons of war,” he said. “There’s got to be restrictions against selling these weapons in the United States.”