Loose in the Trigger(1967)

Original title: Du mou dans la gâchette

Nicolas Pappas and Léon Dubois, two particularly calamitous killers, arrive in Paris, where a gangster boss in need of "staff", Jo Laguerre, hires them to cover the escape of the perpetrators of a hold-up. They get away with it as best they can and then find themselves in charge of liquidating a certain "Magnum"...