Posted at blog.joehuffman.org by Lyle at UltiMAK is this entitled "The Sound of Gun Fire from Downrange." I posted a comment there that I append to his below.
Be certain to go to the site and watch the video. If you can, set up a means of similarly training yourself and your buddies to know the sounds and sights of small arms firing.
It is important to know these sounds (and to experience the light effects of weapons fired at night) if you wish to stay alive when the range goes two-way.
I've long been disgusted by Hollywood's portrayal of sounds. Sounds in space, sound traveling at the speed of light, and the ridiculous sounds of gunfire made up in a studio. Even the news services will often do a time-shift, to synchronize the sound of a distant event with the video even though anyone who's been alive long enough to understand what they're seeing on TV knows that sound and light travel at different rates. I just, do, not, get why TV and movie people have to screw up reality so much. Far from adding anything, it subtracts from the final product.
For example, I think the long delay in the sound of a distant explosion at Boomershoot makes the experience more awesome. It adds to the perception of enormity. The movie, "Band of Brothers" is an attempt to show it like it really was, and for the most part they seem to have done a good job. Not when it comes to sound editing though. Super-sonic bullets whiz by, "whoosh-whoosh, zip, zip" and so on, and of course the sound always travels at the speed of light. It's taking a serious subject and turning it into slapstick.
In the interest of universal understanding, I made this recording of .308 rifle fire from about 380 yards while setting up some rifles for Boomershoot. The camera is about 20 yards from the targets (yeah, I was holding the camera, but I was behind a hill from the gun and in radio communication with the shooter-- completely safe).
Each shot delivers multiple sonic effects or events. First is the "CRACK-hiss" (mini sonic boom) from the bullet. Take the sonic boom from a jet flying over, speed it up a few octaves, and you'll have about the same thing. That bit is interesting in that it does not come from the gun, but from the bullet. You have no sense of the direction from which the bullet came. Imagine standing in the water on the shore of a lake and feeling the wake from a passing boat on your legs. From that sensation alone, you have no idea of where the boat came from, and little or no information about its direction of travel. The bullet's wake, as sound, gives you no more information-- just a "snap" that seems to come from nowhere. Next is the sound of impact, which is only audible in the first shot in this recording. Then comes the "boom" from the muzzle blast, followed by the reverberation in the surrounding hills and trees.
Note that the reverb almost seems louder than the crack-boom. That's due to the AGC (Automatic Gain Control) circuitry, A.K.A. "compression" built into the camera. The initial crack drives circuitry into gain reduction, and the gain comes back up for the reverb. To get the relative levels of the events portrayed accurately, I'll have to take a full-range stereo recorder into the field on another day and use its un-compressed level mode. If you have some nice speakers (and pretty powerful, as the dynamic range is quite wide) you’ll hear it as if you were actually standing there.
Regular CD audio has a dynamic range of about 100dB, IIRC-- close enough. This recording isn’t all that bad, though. Crank up the volume, use good speakers, and boost the bass to get the full effect (the mini electret mic on the camera isn’t great for bass response);
In 1942, the United States Army made a training film, of which I have a dubbed VHS copy, that illustrated this for soldiers. They covered the sound effects of weapons large and small on the battlefield from M1911 to 155mm howitzer, at all ranges -- origin, overhead, and impact area.
I have trained folks in this by positioning them behind a backstop during the daylight at a local range, and also by letting them experience night fire from downrange by firing semi-auto rifles of different types from a fixed rest (much like the wooden framework used in infantry training for overhead fire, although in this case they are standing to side so they can both see and hear weapons effects at one hundred yards).
Note: in the night firing you learn very quickly which so-called flash suppressors actually suppress flash.