Herrrmmm; a human experiment is in order. The round buzzing by was definitely noticable once the cover was installed.
So I propose that you shoot towards someone blindfolded; whilst you move around him in random directions, and see if he can spot your general location. If the gun was absolutely dead silent, I'd bet the high pitched sound of that round whould pinpoint your general location by better than 45*. I'm really, really interested in knowing if I'm correct.
Btw, I pm'd you about this stuffs.