And nothing is being done about it that anyone can tell:

From 2014 to 2016, across 15 countries in North America, Central America, and the Caribbean, 50,133 Guns that originated in the United States were recovered as part of criminal investigations. Put another way, during this span, U.S.-sourced guns were used to commit crimes in nearby countries approximately once every 31 minutes.

Certainly, many of these U.S.-sourced crime guns were legally exported and were not diverted for criminal use until they crossed the border. The United States is a major manufacturer and a leading exporter of firearms, legally exporting an average of 298,000 guns each year. However, many of the same gaps and weaknesses in U.S. gun laws that contribute to illegal gun trafficking domestically likewise contribute to the illegal trafficking of guns from the United States to nearby nations.

[…]

According to data from the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF), of the 106,001 Guns Recovered by law enforcement as part of a criminal investigation in Mexico from 2011 to 2016 and submitted for tracing, 70 percent were originally purchased from a licensed gun dealer in the United States. These U.S.-linked guns likely represent only a fraction of the total number of guns that cross the southern border, as they only account for those guns that were both recovered by law enforcement during a criminal investigation and submitted to ATF for tracing. Other estimates suggest that close to 213,000 firearms are smuggled across the U.S.-Mexico border each year. According to the U.S. Government Accountability Office (GAO), nearly half of the U.S.-sourced guns recovered in Mexico are long guns, which include high-caliber semi-automatic rifles, such as AK and AR variants. This is a concern for Mexican law enforcement officials, who have reported that assault rifles have become the weapons of choice for Mexican drug trafficking organizations, in part because they can easily be converted into fully automatic rifles.¹ The GAO also reports that, from 2009 to 2014, the majority of the crime guns recovered in Mexico that were originally purchased in the United States came from three southern border states: 41 percent from Texas, 19 percent from California, and 15 percent from Arizona.

The impact of rampant gun trafficking from the United States to Mexico has been devastating. In 2017, Mexico reached its highest level of homicides in the past 20 years, with a rate of 20.5 homicides per every 100,000 people.¹² While this figure is partly driven by high levels of impunity for criminal behavior, access to firearms has also been a key driver of the increase in homicides. In 1997, 15 percent of Mexico’s homicides were committed with a gun, yet, in 2017, that percentage rose to roughly 66 percent. The use of firearms during violent robberies has also increased. In 2005, 58 percent of robberies were committed with guns; in 2017, this figure increased to 68 percent.

Read the full report (with source notes) here:

Beyond Our Borders: How Weak U.S. Gun Laws Contribute to Violent Crime Abroad (Center for American Progress, 2 February 2018)