I believe that sound travels at around 1050 ft per second (give or take) if the shot was fired 2 miles away and it was in the air for 10 seconds the muzzle report would be well behind (plus was a moderator fitted) but it's a question of how far before the round slows to sub sonic and whether that would make enough sound to be audible from the position of the target.
It was at this point that I broke out in a sweat and realised why I failed my maths exam in school. I'm going to have a cup of tea and a lie down now but if anyone fancies doing the sums I'd be interested to know the outcome smile

Rust never sleeps !