I'm not doubting your claim but do you know whether they were using subsonic rounds. Because, at least in the first video, it sounded as if the round went supersonic.
As far as knives go I have no problem with them I just can't really see them being used practically, for stealth killing with a knife maybe you could come up behind the enemy slit his throat while you're covering his mouth and once he's dead lie him on the ground. Not practical but at least it's moderately stealthy.