Mexico’s defense secretary says nearly half of the .50 caliber rounds seized from cartels since 2012 can be traced to one place: the U.S. government–owned Lake City Army Ammunition Plant outside Kansas City. Of roughly 137,000 .50 cal cartridges Mexico has confiscated, about 47 percent came from Lake City and were later sold through civilian gun shops in the southern United States before ending up in cartel arsenals. Those same rounds have also been used in U.S. mass shootings. Since President Claudia Sheinbaum took office in 2024, Mexican authorities have seized about 18,000 firearms—nearly 80 percent traced back to the U.S.—including Barrett .50 cal rifles, grenade and rocket launchers, and machine guns. Sheinbaum says her government will press Washington on how weapons and ammo built for America’s military are leaking into Mexico’s criminal wars.