That's the classic 1903 silent film. It had a startling end with a deadpan faced cowboy points his revolver at the audience and begins firing. I never noticed until recently that he's firing in the double action mode. Double action revolvers were around when The Great Train Robbery was filmed and were available even during the Civil War, but what gun did he use? It's from 11:26 onwards.
The Great Train Robbery
The Great Train Robbery