Lets put this into some context. From this website
http://www.freehearingtest.com/hia_gunfirenoise.shtml we see that a typical .223 Remington or 5.56mm gunshot will be 155.5 dB. A person with good hearing can hear a sound as low as 10 dB and a whisper or wrist watching ticking will be around 20 dB.
A PC fires a shot from their M16 and you want to find out if a group of bad guys will hear the gunshot where they are.
The bad guys are 2325m away. 155.5 - (20log(2325)+11) = dB at there location. 155.5 - (67+11) = 77.5dB. They are going to hear it.
A typical suppressor lowers the sound level by -28dB to -35dB so this will help out.