Now, I could be wrong on this, but i think that the reload sound fore the new m16-a2 also sometimes plays the reload sounds for the M4A1, for example when you chamber a round, it almost sounds as if the new M16 sound effects are playing over the top of the old M4A1 sound effects, but it doesn't seem to always be like that, I didn't notice it at all in offline mode when i was testing the gun but I noticed it a few times on live servers and when watching other people streams or videos.