"The whole nine yards"

The phrase dates to the mid-19th Century, long before machineguns of any kind and is most likely about tailors making clothing - and including all 9 yards of a standard bolt of cloth in whatever piece of clothing, when less would have done better - hence, taking something as far as you possibly can, for no real purpose except to give it your all.

Some people say it dates back to when square-riggers had three masts, each with three yards supporting the sails, so the whole nine yards meant the sails were fully set.