Speed of Sound
Also: Mach 1
Roughly 1,125 feet per second at sea level and varying with temperature, the speed that marks the boundary defining transonic and subsonic bullet flight.
The speed of sound is the rate at which a pressure wave travels through air, about 1,125 feet per second at sea level under standard conditions, and it is the reference known as Mach 1. The value depends mainly on air temperature rather than pressure, so it rises in warm air and falls in cold air, which matters for long-range shooters chasing the last few hundred yards. A bullet’s velocity is often compared directly to this number to describe what regime of flight it is in.
While the bullet stays well above Mach 1 it is supersonic and flies predictably. As retained velocity drops toward the speed of sound the bullet enters the transonic zone, where shifting airflow can disturb stability and open up groups, and below it the bullet becomes subsonic. Because the local speed of sound moves with temperature and altitude, shooters often track it alongside density-altitude when planning shots at extreme distance.