Subsonic Loads

Subsonic loads refer to those whose velocity is less than the speed of sound. Not all "subsonic" loads are noted as such in the data, because the cartridge is not capable of producing supersonic velocity. An example is .32 S&W. All data in this caliber is subsonic but is not normally tagged with the name subsonic. In 9mm, most loading data are supersonic. Some data is shown that is subsonic. These loads are noted as subsonic. Most rifle loadings are all supersonic, so subsonic loads are specially down-loaded to stay below the speed of sound.

The noise that shooting makes has two components, the noise of the hot gases escaping the muzzle and sometimes flashing as they hit the atmosphere (muzzle blast), and in the case of supersonic loads the crack of the sonic boom as the bullet breaks the sound barrier. Subsonic loads do not have this second component of noise. As a side note, if a silencer is attached to the gun it will only suppress the muzzle-blast noise. It cannot suppress the supersonic crack. For this reason people shooting with a silencer prefer subsonic loads, even when shooting a rifle.