Has to do with how much a concrete trucks will hold ...
not exactly considering that concrete truck capacity was as small as 4.5 yards when the term was supposedly coined and now they are as big as 12 yards.
there have been claims that it's a sarcastic phrase from american football when a player falls just short of the 10 yards needed for a 1st down.
i don't remember seeing a 27 foot length of m-2 ammo come out of a fresh box...105 rounds of 50 cal ammo is all the little green can held...for aircraft the belts were linked together.
i've seen/heard of a reference to the length of a belt of machine gun ammo for spitfires being 27 feet...
truth is, no one really knows where it started.
