The way I understand it, the noise a gun makes when fired comes from
Hammer snap, action cycling, etc… anything that moves or rubs as the weapon operates.
Release of gas pressure as the bullet exits the barrel, and the characteristics of that pressure impulse. This is affected by the actual pressure at the muzzle and how quickly (and along what paths) it’s released. Powder charge, barrel length, and any muzzle device all are factors - not just bore diameter.
Sonic crack of a supersonic bullet.
If you just wanted to know which of two particular weapons was louder, you could test with a quality peak-holding sound-pressure level (SPL) meter at some given distance. However, things like the characteristics of the report, likelihood of echo, and audibility at a distance can change minute-to-minute based even on the terrain around you and the atmospheric conditions.
So what if both weapons were both in the exact same terrain such as in the mountains or in an urban city and with the same atmospheric conditions, what would be louder than?
you should search the archives. There was just a thread about this within the past month. Lots of info in that one.
OH heck, I dont even remember if it was in the general forum or AR general.
Barrel length has a lot to do with it. Where you’re standing relative to the rifle has a lot to do with it. Muzzle device has a lot to do with it. Are you talking sound relative to the shooter, people standing around, or in general?
Most people will say the M4 is louder than the AK, but the M16 might be quieter than the AK. And as said before, the AR is more of a crack compared to the boom of an AK.
I’ve never compared at a distance, but my brother tells me the AR carries more.
Yes the 7.62x39 is louder up close, but the crack of the 5.56 will be heard farther in stock barrel lengths
On another note, some forms of auto racing is a lot louder than shooting normal cal.s, but most people don’t wear ear protection while watching auto racing.