Thanks.
So, did WWII aircraft use cotton-belted ammuntion or metallic links?
No WWII historian or M2 expert by even the faintest of stretches.
But. considering the need for mounting the .50 on both wings, flammability issues, and feeding from both sides, the reversible nature of later linked ammo (the need to de-link and eject) would strongly suggest only metallic linked belts were used. Jams were frequent enough, how would you get rid of cloth belts in an aircraft wing space? Or link successive belts into a continuous one?
Not being an Gen-x/y/z type that Googles everything, I strongly suspect that the general feed pawl dimensions of the M2 did not very too much from the very early guns that "might" have used cloth belts.
All great fun, but if you wanted to retry the arithmetic with a nominal spacing between cartridges of about 0.2" (which my fading mind's eye says is about right for linked .50 BMG), the total length just might come up close to the magic "9 yards".
Hey, it makes for a good yarn to babble about.