Flash in the pan – Going off half-cocked – Lock, stock and barrel
The kind of gun you see in western films, where the gunman can quickly load a set of metal cartridges into his handgun, only came into use in around the 1830s. In Regency times, guns were fired using a flintlock mechanism. Our heros (or heroines) would have used a pistol something like this.
The stock is the handle and other wooden parts, the barrel is the tube the pistol ball travels down when it is fired, and the ‘lock’ is the firing mechanism. Each part was made by a different craftsman, so ‘lock, stock and barrel’ means having the whole thing, complete with all its parts.