I'm glad Larry came in and highlighted the airflow issue. I have indeed had supersonic cracks with subsonic ammo at cooler temperatures. Some cracked loudly, some pretty quiet but still audible. That same ammo was completely quiet on a warm evening. Velocity is a nominal 1050 fps and that's what I measured with it. Not a string, just one or two to check the chronograph and to see what the ammo was actually doing. On the cool evening the speed of sound would have been around 1120 fps I think it was.
But the real question is, just how much effect on accuracy does it have?