Considering the term "whole 9 yards" didn't show up til the 70s, I doubt very much it is war related. Too many urban myths surround that phrase. It's relatively modern, NOT WW2 related, NOT sail-ship related.
Just as an aside.
EDIT: Well the problem with light ammo loads is this:
These planes (f6f and f4u) have relatively medium ammo loads, as-is. I often need all of the ammo just to get a few kills, and that's WITH firing conservatively, and WITH picking my shots well.
I have (many a time) unloaded every last shot into a bomber (or formation) and not gotten a single kill. In an f4u I unloaded every shot into 3 lancs, making 7 passes or more, and ended up getting only 3 assists, with millions of hit sprites.
So *IF* you have to get up there in a hurry, the lesser ammo load (I'm thinking about equivelant to P40E, right?) you'd not get any kills.
Having considered that, I'm all for it, if you can prove it was very common. You have to prove what time frame it was used in (and if the aircraft we have match that time frame), what groups used it, how many used it, how often they used it, and how widespread that use was across the entire fleet. Hell, 1/3 the total 109G-6s had 30mm, but our model doesn't have it anymore, because it's a mid-era G-6. Under the same logic, we have to make sure things like this reduced ammo fit the time frame for the f4us and f6fs, and other things.
If you have all that info and it all "gels" with the models we have, then I'm all for it!