M249 bullet casings

[Ronin4862]

The M249 ejects two types of brass: bullet casings and some type of chain I suppose.
So for 10 bullets fired we get 5 shells and 5 chains.
It would be correct to get 10 shells and 10 chains; double the brass in other words.

[SamVanheer]

This is intentional. The M249 alternates between ejecting one or the other. Ejecting both creates too many temporary entities which could cause them to become invisible if too many temporary entities are created at the same time (e.g. if you continuously fire the M249 until you use up all ammo you will create too many).