Here's a link for you.
http://www.fas.org/man/dod-101/sys/land/m2-50cal.htm
This is not something that just falls out of your pocket, and you fail to notice. Something really fishy is going on here.
After WW2, my wife's grandfather was sent to dump crates of garands still packed in cosmoline in a creek. A few months later, the Korean war broke out and he was sent back to retrieve them.
I've always wanted to know where that creek was in case they missed a couple.
I had one of those (as a civilian) shoved in my face while violating the curfew in Saigon in 1966. It sure has a sobering effect.