Subsonic 300 In Hot Weather

[Artful]

If you notice the noise you hear may or may not be sonic boom (ie breaking the speed of sound) as you approach the speed of sound you enter the transsonic area in which the noise of the projectile increases as the bow wave starts to build infront of your bulet.

http://guns.connect.fi/gow/highpow.html

Above is a nice chart relating to bullet noise and velocity that is worth looking at. Transonic is between 1,000 fps and 1,300 fps, and the noise level goes up very, very steeply between those velocities. The noise goes up very slowly between 700 and 1,000 fps, and then takes a dramatic jump to between 90 dB (which is virtually nothing) to almost 140 dB (which is major noise) at 1,300 fps. The noise levels were measured 10 meters to the side of the bullet's flight path. It is nice to see some serious, authoritative studies done on the subject. Measurements were taken all the way up to 3,800 fps, where the noise level increased slightly from that which existed at 1,300 fps.

For measuring this bullet flight sound diagram every .308 cartridge was handloaded prior to each shot. A T8 Scout suppressor is attached to a BR varmint rifle. Sound meter remote readout and loading equipment are shown beside the rifle. Contrary to previous belief it was found, that in practise the speed of sound (Mach 1) was not any sudden threshold to sonic crack. Results of these as well as of other Suppressor Project experiments are published in Alan C. Paulson's book Silencer History and Performance, Vol. 1