We used to be across from a Gun Club. There would be a shot and the the echo. Sounds like two shots.
During Garand matches, when we are in the pit, pulling targets between shots, there are three distinct sounds. The first is the whip-like crack of the round going overhead (supersonic speeds), the second is the whump of the round against the backdrop (immediately after the crack), and then the last is the sound of the firing of the round finally reaching us as it had to travel 200 yards.
It was "CRACK-WHUMP-BANG". Kinda cool, actually.