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Started 20-Nov by gatnerd; 551 views.

20-Nov

In Emeric's fantastic GPC paper, he had raised the issue of different rounds being louder and more suppressive down range.

Well on Youtube today I stumbled across a video that documents this down range effect, which I thought would be of interest.

What does it sound like to be shot at? In today's video we show you what bullets sound like at various distances from various weapons. There is much that can...

5.56 vs 7.62x39 at 500m (~12 min mark) is especially notable - the x39 supersonic crack is indeed louder at 500m.

Now the test is imperfect, in that its for fun with a dude firing standing at a berm 500m away. So no doubt there is quite a bit of variation with how close the bullets pass over the speaker / camera.

But still, pretty neat.

21-Nov

gatnerdsaid:In Emeric's fantastic GPC paper, he had raised the issue of different rounds being louder and more suppressive down range.

Well on Youtube today I stumbled across a video that documents this down range effect, which I thought would be of interest.

I noticed that video on YouTube earlier today but did not then have time to watch it.

I disagree that it supports Emeric's premise that louder rounds are more suppressive.

The reaction of the downrange guys was pretty much the same regardless of caliber.

The notable exception was the .30-06 ricochet at 12:52, which caused them to duck.

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I agree the test is imperfect. Way too much f&@king clowning around for my tastes.

And the inclusion of a .45-70 rifle and a 40mm grenade launcher was just plain silly.

21-Nov

stancristsaid:I agree the test is imperfect. Way too much f&@king clowning around for my tastes. And the inclusion of a .45-70 rifle and a 40mm grenade launcher was just plain silly

To be fair, I doubt they read Emerics paper prior to testing ;-)

Still, for the price we paid for the testing (free) I think we got more than our moneys worth.

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.

What was interesting to me, and Im not sure if this was due to distance from the speaker, but .50 didn't seem nearly as loud overhead as we'd imagine give its vast increase in power compared to the other tested rounds.

21-Nov

gatnerdsaid:To be fair, I doubt they read Emerics paper prior to testing ;-)

I'm sure that's true. But in any case, the stated purpose of the test was just to show what different bullets sound like at the receiving end, not to evaluate their suppressive effects.

gatnerdsaid:Still, for the price we paid for the testing (free) I think we got more than our moneys worth.

LOL. I think we got out of that video exactly what we paid for it: Nothing.

The "test" was done by a bunch of clowns, in a rather haphazard manner.

gatnerdsaid: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.

Yes, that is interesting. And to my ears, the 7.62x39 sounded marginally louder than the .30-06 bullets, too.

gatnerdsaid:What was interesting to me, and Im not sure if this was due to distance from the speaker, but .50 didn't seem nearly as loud overhead as we'd imagine give its vast increase in power compared to the other tested rounds.

I agree. For that matter, I thought the .50 BMG bullets didn't even sound quite as loud as the 7.62x39 rounds.

21-Nov

gatnerdsaid: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.

21-Nov

EmericDsaid: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?

22-Nov

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

22-Nov

stancristsaid: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.

22-Nov

mpopenkersaid: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!

22-Nov

Thanks

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

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