Lots of gangster movies end in a shoot-out. Director Ben Wheatley's new tough-guy flick, Free Fire, begins with shots fired—and never stops. The entire movie is a firefight. "It started from reading an FBI transcript of a gun battle in Miami that happened in the 1980s. It was kind of forensic blow-by-blow report," Wheatley says. "It really struck me how different that was from anything I'd seen in the cinema." The concept was so different, in fact, that he decided to make it himself.

Set in a Massachusetts warehouse in the 1970s, Free Fire, out today, barely waits for the credits to finish before the bullets fly. Chris (Cillian Murphy), an Irish gangster looking to buy some machine guns, and Vernon (Sharlto Copley), a dealer looking to sell some, have almost completed the transaction when one of Vernon's men realizes that one of Chris’ goons disrespected his cousin at a bar the night before. At first, the situation looks like it's going to get resolved respectfully—then bang! Before anyone can invoke Mr. Pink's immortal Reservoir Dogs line, "we're supposed to be fucking professionals," everyone scatters...and straps up. From then on out—62 minutes, give or take—it's a hyper-funny, rapid-fire battle to see who can get out of the warehouse alive. As alliances shift and bullets keep flying, the odds of anyone doing so plummet.

But the only one who really had to survive the shoot-out was Wheatley, who had to make sure every shot, both from a gun and captured by his camera, happened in sync. To do that, he drew 1,700 storyboards, built a physical model of the warehouse he planned to film in, and even created a 3-D simulation of the space in Minecraft (using a Blade Runner texture pack) to get every shot right. “We could share that amongst all the people who working on it, and all walk around inside it together,” Wheatley says. “That was really useful.”

More than anything, the Minecraft renderings helped the director determine what size space he would need to film in and what kind of objects he would need to put in it to give his characters proper cover. Because each Minecraft block is the equivalent of a cubic meter, he could calculate how much floor space he needed, as well as the size of the containers, walls, etc. he’d need his various shooters to hide behind. Designing in *Minecraft’*s 3-D space also helped him figure out what each character's line of sight would need to be, which in turn determined—whether they could conceivably hit their target or not.

This blueprint shows where each character in Free Fire had to move to during one 10-minute segment of the movie. The numbers indicate where each "pyro" was placed. A24

Once the whole thing was plotted out, Wheatley and his team were able to scout a location for their shoot(-out): an old factory in Brighton. Wheatley then made blueprints of the space along with his production designer, Paki Smith, that helped dictate where each actor had to go in each scene. (The director likens it to plotting out plays in a game of Madden.) He broke the hour-plus shoot-out into eight segments that represented about 10 minutes of the final film and created a blueprint for each. The blueprints not only described each actor's location and/or destination, but also allowed the crew to follow and film them—and gave the visual-effects team a map for the location of each “pyro” (the small devices that explode during filming to give the appearance of a bullet hitting something).

If that all seems like a lot of work, it was—but it was worth it. It kept everyone exactly where they needed to be and nothing looks faked. "Because it’s in real-time and one space, you can't really cheat as much as you can on a normal film,” Wheatley says. "With this one, if you suddenly jump about, your characters start teleporting around the room—and it breaks the whole thing."