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Point taken. I have not seen or read any evidence of an M249 being found.
Here is a set of pictures that I found pretty quickly. It shows two different firearms, one with a 100 round Surefire mag and a bumpfire type of stock. The other shows two types of magazines for different calibers and what appears to be brass from at least two and likely three calibers on the floor. If I had the original photo's resolution, I could make a good estimate of the calibers, but this photo is not good enough for me. Maybe someone else has a higher resolution version of this photo?
Sure is a whole lot of brass laying around. /s