[LibKill]

Only subsonic rounds lend themselves to being silent. This round is travelling at around 3,000 feet per second. It's probably the 55 grain variety, but it may be the 70 grain weight. Still it's going to make a lot of noise.

It is possible to completely silence the sound of the cartridge from a much higher-powered cartridge.

What cannot be silenced is the sound of a bullet breaking the sound barrier. But, that sound is not very loud, about like a child's cap pistol. A firecracker is very much louder.

[RLK]

In the military we had some very old firing ranges where we sttod down in a pit and raised the targets, then flagged the position of the hit. You could hear a loud crack as the bullet passed overhead.

[e_castillo]

that sound is not very loud, about like a child's cap pistol.

Thats totaly incorrect. A bullet like this makes a sounds almost as loud as the cartridge going off. Ever compared subsonic to a standard round?

[B4Ranch]

http://guns.connect.fi/gow/arcane1.html

Sub-sonic is approx. below 900fps.