Pie-r-square - Handgun Hunting

American Handgunner, July-August, 2003 by J.D. Jones

The speed of sound varies greatly due to temperature. According to my information, altitude under 40,000 feet has insignificant effect on it. I'm told this is the formula the USAF uses to determine the speed of sound, so break out the .99 cent calculator:

Temperature in F plus 459 = ? The Sq. root of ? X 49.06 = speed of sound.

For example: 70F + 459 = 529. Sq. root of 529 = 23 X 49.06 1128.38 FPS -- the speed of sound. The speed gets lower as the temperature drops and higher as it rises. You can find it at any temperature with this formula.

Transonic velocity is important. When a bullet in free flight is in transonic velocity range both above and below the speed of sound, it's subject to forces detrimental to accuracy. Twenty-two caliber match shooters normally use ammunition that is sub sonic to avoid this phenomenon. Long range shooters find if their bullet stays above the speed of sound until it hits the target, accuracy is greatly enhanced compared to accuracy when the round drops through the transonic velocity range and impacts sub-sonic.

The single greatest factor affecting the performance of a given bullet against a given target is simply velocity. The greater the velocity at impact the greater the affect on the bullet and target.