EMMSixteenA4 is just the literation (coined!) of verbalization of the gun the M16A4. Kind of like if I said, "M16A4," to you if you had never heard it before and told you to write it down, you might write "emmsixteen," if you were an idiot, and then if you were a bigger idiot who happens to be semi-fluent in leetspeak you'd write, "EMMSixteenA4".
Because I thought that that gun was cool.
I don't even think it's in service with any military right now though, eheheh.
So unless I become EMMFourCarbine the name isn't exactly what one may call relevant.
People seem to like my username, generally, and I have a lot of social media using it as a handle so switching to my alternate handle ShootTheGlitch would be tough, even as dumb as I think EMMSixteenA4 to be.