Now, I could be wrong on this, but I think that the reload sound for the new m16-a2 also sometimes plays the reload sounds for the M4A1 at the same time as the new sounds, 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.