Gunfire audible range

[Legbreaker]

Yes, it really is as long as a peice of string.

As has been pointed out, wind, rain, terrain, background noise and about a billion other factors are in play. However, the larger the calibre of the weapon, the greater the volume (usually).

For example, a 7.62mm x 51 gunshot can be heard very well up to a couple of miles in average conditions (ie countryside with normal sounds) while a 5.56mm might be just half that.

The actual sound of the projectile ripping through the air on the other hand is something else (remember, most military rounds are supersonic and have a supersonic "boom"). When a shot is fired at, or at a target nearby, it is relatively easy to hear, and with minimal training estimate to a reasonable accuracy the range, and even general location of the shooter (in a similar way that distance to lightning can be estimated).

For your example of a 15 x 4km island, I'd say most of the enemy forces can either hear, or will soon know about the gunfire (I presume there's locals living on the island too?). Single shots might be ignored (provided they're the only one fired within half an hour or so and could be passed off as a car backfiring for example), but bursts are DEFINATELY going to get noticed.

The best chance of the PCs remaining unnoticed for some time is to a) avoid combat (or better yet contact of any type), or failing that, use subsonic rounds from preferably silenced weapons (or just knives, axes, fists, harsh language, etc). They insist on assault rifles and up and they're going to be heard.

[Graebarde]

There are a number of variables that must be taken into account for sure. One not mentioned is temperature. While it's not gunfire, I do recall overhearing a conversation that took place a mile away. The folks were talking plainly. It startled me to hear them talking as I had just come out of the house. Conditions: Calm, night, and -40F. The only time it happened, but it did. Spooky too.

And as has been stated, gunfire, at least the muzzel blasts, can be heard at some distance. I think the chart is a good starting point, and for game use quite good. As the HoG, you can always add or subtract from the ranges. I have heard gunfire at ranges over two miles from high-power rifles.

[pmulcahy11b]

Also remember that as you watch TV, Movies, YouTube, etc -- you are almost never hearing what gunshots really sound like. The standard report for a .357 Magnum that the industry uses was done with half a stick of dynamite. Gunshots are surprisingly "quiet" (ie, not as loud as you expect, not necessarily quiet) when you hear them close up -- yet they echo over long distances.

And then there is the opposite grievance of mine -- silencers in movies and TV. They are NOT as quiet as portrayed on movies and TV -- the typical silenced round sounds like a .22 Long Rifle round being fired, better ones sound like a cap gun, and I once was standing beside someone firing an MP-5SD -- it sounded like a cork being popped from a bottle of champagne. None of that high-pitched thweep-thweep-thweep -- no silenced firearm in the world sounds like that. And don't forget that silenced semiautomatic or automatic weapons have bolt clatter -- you will hear the mechanism of the weapon working. Silencers do hide most of the muzzle flash (though some oil-based or water-based silencers will spit a very small cloud of water or oil), help the sound not carry as far, and if you hear them, make it difficult to determine where the shot came from.

Most of the rounds that make noises that carry a long way are supersonic (most bullets are), but rounds like the .45 ACP, which are subsonic, won't. Most of that crack you hear over long distances is not from the weapon being fired -- it's from the round breaking the sound barrier. Just as an aircraft breaking the sound barrier will produce a shock wave (the sonic boom) that will carry a long way, so will a bullet. Subsonic bullet reports do not carry as far.

[pmulcahy11b]

Originally Posted by Graebarde

There are a number of variables that must be taken into account for sure. One not mentioned is temperature. While it's not gunfire, I do recall overhearing a conversation that took place a mile away. The folks were talking plainly. It startled me to hear them talking as I had just come out of the house. Conditions: Calm, night, and -40F. The only time it happened, but it did. Spooky too.

It also depends on the terrain conditions -- a shot is more likely to be heard a long way away if you fire it in the Grand Canyon than if you fire it deep inside Yosemite. There's an interesting room as Bell Laboratories that they use to test certain sound equipment -- you can shout in it and almost not even hear yourself, because of the tiling on the walls. There's another one where if you stand in a certain place in the room you can whisper and no one will hear you unless they are standing in another certain part of the room -- where your whisper will sound as loud as a shout. Anywhere else in the room, you'll hear nothing.

[Grimace]

Being in Montana where you hear a lot of gunfire in the fall when hunting starts, I can say the following:

Average light firearms, such as a .22.. you're only going to hear it about a half mile away...maybe a bit further (sorry, this is going to be in Standard measurements, not metric...my brain doesn't work well in metric at night). Hunting rifles can generally be heard up to about 3-4 miles away. That's hunting rifles fired in the forests and I'm standing out in the open fields. It might be the echo giving it away, but you can pretty distinctly hear the muzzle discharge too. When I'm also in the forest, and the rifle discharge is in the forest, cut that down to about a mile, maybe a bit more.

I'm about 2 miles from a rock quarry where they blast about every day. Due to the duller nature of the explosions, and the fact that they're buried munitions, I can hear them when I'm outside, but not inside. Some days I can even BARELY feel slight taps in the ground when they blast. Being a once-miner, I know how powerful those blasts are up close. I've been too close to one before and was stunned by the concussive blast of one. An exposed explosion, I would imagine, could probably be heard for much, much further.

Now I'll also mention that I KNOW humidity plays a big part in how the sound travels. I moved from a very wet area, where the sounds of things were pretty quickly stifled over very short distances, to a pretty dry area (average humidity is about 16%) where sound seems to travel quite well. So I've noticed a difference in that regard.

[headquarters]

I remember being a mile - mile and a half from a range where our platoon was doing target practice .Some cliffs and a little vegetation and terrain between us .i. e not open .

Under those conditions the steady fire sounds a little like the drone of a waterfall in the distance ..in a way.

Heard it good though

[pmulcahy11b]

Ever hear a Vulcan from a distance? Sounds like a lawnmower...

[General Pain]

Ffffing good question by the way. Can't belive I never posted this myself.

Here are some quick google results:
http://en.wikipedia.org/wiki/Sound
http://en.wikipedia.org/wiki/Acoustics
http://www.freehearingtest.com/hia_gunfirenoise.shtml
http://www.acoustics.org/press/146th/schomer.htm
http://www.thehighroad.org/showthread.php?t=226357