I think that the term lock, stock and barrel came from the days of the early western frontier when a business (such as a general store) would sell out to another. Lock being the premises and fixtures, stock being the hard goods and barrel being the dry goods and perishables. Ergo, “He bought the business, lock, stock and barrel”.
At least, that’s what I was told when asked about the origin of the term. Nowdays, it seems to be said to be a “turn key operation”.[/quote]
Aren’t all three simply parts of a gun? If you have the lock (the firing mechanism), stock (the main body of the gun) and barrel (the, uh, barrel of the gun), then you have the entire gun.