Le vieux fusil

Le vieux fusil English title The Old Gun aka Vengeance One by One is a 1975 French film directed by Robert Enrico, and starring Philippe Noiret, Romy Schneider and Jean Bouise. It won the 1976 Csar Award for Best Film, Best Actor and Best Music, and was nominated for best director, supporting actor, writing, cinematography, editing and sound. The film is based on the Massacre of OradoursurGlane in 1944.

Dandieu decides to kill as many Germans as possible to avenge his family. He takes an old shotgun he used as a child while hunting with his father and starts to kill them one by one. They begin to think they are surrounded by many partisans and do not realise that he is, in fact, the only one, taking advantage of his knowledge of the secret passages within the chateau. He beats one of the SS men to death, shoots some of them and lets two of them drown in the well, where he closes the grid, preventing them from escaping.With no more cartridges for the shotgun, he finds the flamethrower which killed his beloved wife and uses it to kill the SS officer as he is about to commit suicide standing in front of the twoway mirror. The film ends with the liberation of the place by the French Resistance. ........

Source: Wikipedia