I’ve always been interested in the origins of some of our most common expressions. One explanation for “the whole nine yards” came from some World War II fighters carrying 27 feet (nine yards) of machine-gun ammunition. When they came back empty, the ground crew would exclaim “He gave them the whole nine yards.”
I’ve just read how several common expressions have come from flintlock firearms. To prepare to fire, the hammer is first cocked partway so gunpowder could be sprinkled onto the priming pan; if the hammer wasn’t then cocked the rest of the way, the gun would go off “half-cocked”.
When the trigger was pulled, a piece of flint would strike a metal plate, creating a shower of sparks to ignite the powder in the pan. But if the charge inside the barrel wasn’t ignited, the result was a “flash in the pan”. When that happened, no one knew if or when the gun would go off — it was “hanging fire”.
The firing mechanism was named the lock, one of three main parts — for a complete gun, you had to have a “lock, stock and barrel”.
The English language owes a lot to the early gun-makers!
The original entry is in the book The Greatest War Stories Never Told by Rick Beyer (Collins, 2005), page 46.