The plot of Free Fire is like a Syd Field screenwriting exercise: “Set a gunfight in one room. Make it last 80 minutes. One person lives.” The options include Armie Hammer as a cocky arms dealer, Cillian Murphy as the gun-buyer, Brie Larson as The Girl, Sam Riley as a dirtbag and Enzo Cilenti as the hothead who shoots him, setting off the gunfight. It’s in a warehouse with varied terrain—it gets hairy when both sides get fired on by a third set of shooters—and it has a breezy sense of humour, so it’s entertaining. But the longer it goes, the grosser it gets, fulfilling a horror-movie exploding-head fetish for director Ben Wheatley. Fun if you like this sort of thing, sad for Larson fans still smarting from Kong.