Cartel Land Directed by Matthew Heineman. Rated R. Opens Friday.

The devastating effects of drug cartels in Mexico have been explored in a number of documentaries in recent years, but Matthew Heineman’s Cartel Land takes a new approach, focusing not on cartels or government officials, but on two very different vigilante groups. The impacts of the two groups are far from equal, which makes the movie a little lopsided, as it moves from the Arizona-Mexico border, where a group called Arizona Border Recon patrols for drug smugglers, to the Mexican state of Michoacán, where the vigilante group Autodefensas becomes so powerful that it resembles the heavily armed paramilitary cartels it’s ostensibly trying to combat. Heineman gets astonishingly close to heated gun battles in Mexico, and he uses careful editing to show how both groups are ultimately almost as ruthless and menacing as the criminals they are up against. Cartel Land is a vivid and sometimes infuriating portrait of a seemingly unwinnable battle.