Major GOOF spotted. Milady is shown holding a percussion cap pistol
MAJOR GOOF SPOTTED.
In the scene where Milady (actress Faye Dunaway) pulls a pocket pistol out of her hand fur muff to assassinate the Duke of Buckingham, it is shown to be a percussion cap pistol. You can see the pistol even closer in the duke's hands and there is absolutely no doubt it is a percussion cap.
The percussion cap succeeded the flintlock in the 1830s. Percussion caps were far more effective and reliable than the flintlock. Ironically, the percussion cap ignition system was short-lived, only about forty years or so. It's ignition principle continued in the self-contained metal cartridge and bullet combination that appeared just before the American Civil War, technologically advanced during the war, and was perfected just after the war and is still in use today.