I was just doing some double checks on my gear this weekend and looks like I did indeed lose an M4 magazine. It's an old STAR airsoft 30 round plastic mag. It's grey and most likely has some OD 100MPH tape at the base with a "B" on it for Bigfoot. Most of my mags have that. No biggie if nobody found it as it's from 2008 and only cost me like $5 at the time. Still, it would be nice to keep the set together.
EDIT: It was lost in the village during the night game Saturday.