gatnerd said:

The most interesting data point I think is that 7.62x39 - despite having worse ballistics then 5.56 (or perhaps because of having more drag) - had a louder supersonic crack then 5.56 at 500m.

The measurements made by G. Oberlin (from APG) on bullet "flight noise" show that as long as the bullet is supersonic, the main parameter for the bullet noise is its diameter, and in the various "suppressive" tests, the 7.62x39 mm was rated "as suppressive" as the 7.62x51 mm.

The second parameter is "how far you are from the bullet path".

According to the formula given by G. Oberlin, the sound pressure of a M855 traveling at 400 m/s is 150.9 dB at a distance of 1 m.

A M80 bullet traveling at 400 m/s is producing 153.5 dB at 1 m (+2.6 dB, which is significant), or 150.9 dB at 1.5 m.

A M33 bullet traveling at 400 m/s is producing 156.3 dB at 1 m, and 150.9 dB at 2.4 m.

So, bigger bullets generate more noise at the same "miss distance", or the same noise at slightly longer distance, but here we are talking about an (uncontrolled) miss distance of several meters, so it's difficult to draw conclusions.

EmericD said:

According to the formula given by G. Oberlin, the sound pressure of a M855 traveling at 400 m/s is 150.9 dB at a distance of 1 m.

A M80 bullet traveling at 400 m/s is producing 153.5 dB at 1 m (+2.6 dB, which is significant), or 150.9 dB at 1.5 m.

A M33 bullet traveling at 400 m/s is producing 156.3 dB at 1 m, and 150.9 dB at 2.4 m.

So, bigger bullets generate more noise at the same "miss distance"

On the battlefield, different caliber bullets won't pass by the target at the same velocity.

For example, 5.56x45mm M855 is going 400 m/s at a distance of a little over 400 meters.

At the same distance, 7.62x39mm PS is moving at only ~340 m/s.

And 7.62x51mm M80 is considerably faster, doing about 470 m/s.

At a "miss distance" of 1.0 m for each of the three, what would their sound pressures be?

from what I've seen, a 9x19mm bullet traveling at a slightly less than 400 m/s (from a carbine) generates about 1-3 dB louder crack compared to the 5.45mm bullet traveling at twice that velocity

measured at about 2 meters off the line of fire

stancrist said:

On the battlefield, different caliber bullets won't pass by the target at the same velocity. For example, 5.56x45mm M855 is going 400 m/s at a distance of a little over 400 meters. At the same distance, 7.62x39mm PS is moving at only ~340 m/s. And 7.62x51mm M80 is considerably faster, doing about 470 m/s. At a "miss distance" of 1.0 m for each of the three, what would their sound pressures be?

Hum, I don't know where the numbers used in this video game came from (they look very wrong), so I'm going to use values I'm more familiar with:

• M855 from a M4; 400 m range (ICAO atmosphere); residual velocity 533 m/s; 151.8 dB (0.777 kPa) at a near miss distance of 1 m.
• 7.62x39 mm PS from an AK; 400 m range (ICAO atmosphere); residual velocity 400 m/s; 153.7 dB (0.967 kPa) at a near miss distance of 1 m.
• DM41 from a 20" SCAR-H; 400 m range (ICAO atmosphere); residual velocity 554 m/s; 154.5 dB (1.060 kPa) at a near miss distance of 1 m.

mpopenker said:

from what I've seen, a 9x19mm bullet traveling at a slightly less than 400 m/s (from a carbine) generates about 1-3 dB louder crack compared to the 5.45mm bullet traveling at twice that velocity measured at about 2 meters off the line of fire

The theoretical values are :

• 5.45x39 mm 7N6 traveling at 800 m/s; 151.9 dB (0.785 kPa) at a near miss distance of 1 m; 147.4 dB (0.467 kPa) at a near miss distance of 2 m.
• 9x19 mm traveling at 400 m/s; 155.9 dB (1.242 kPa) at a near miss distance of 1 m; 151.3 dB (0.738 kPa) at a near miss distance of 2 m.

measuring sound overpressure is very difficult outside laboratory conditions!

Thanks

a bit of OT: have you seen my PM about the WW1 era Winchester 1907 used in France?

This is why I wear the good electronic ear pro that can give me decent enough auditory cuing of direction and type of fire.

It also makes the big round noises less scary...

Someone should maybe study whether the effects are the same with good electronic ear pro.

I am willing to bet you'd get different results but wouldn't dare guess what the difference would be.

EmericD said:

M855 from a M4; 400 m range (ICAO atmosphere); residual velocity 533 m/s; 151.8 dB (0.777 kPa) at a near miss distance of 1 m.

7.62x39 mm PS from an AK; 400 m range (ICAO atmosphere); residual velocity 400 m/s; 153.7 dB (0.967 kPa) at a near miss distance of 1 m.

DM41 from a 20" SCAR-H; 400 m range (ICAO atmosphere); residual velocity 554 m/s; 154.5 dB (1.060 kPa) at a near miss distance of 1 m.

Thank you.  Those numbers seem to roughly correlate to the "500 m" results (actual distance was 450 yds -- a shade over 400 m -- according to Garand Thumb), so perhaps the video test was not so bad.