In this method, range is determined by counting the seconds between the time that you see the flash and when you hear the sound of the gun firing. Count one-thousand-one, one-thousand-two, etc., with each count being one second. Since sound travels through the air at a speed of about 330 meters per second, each second you count equals 330 meters.
To determine the range to a firing weapon, watch for the flash of the weapon when it fires and start counting seconds immediately. The number of seconds you count, multiplied by 330, will give you the approximate range from the target to your position. If you must count higher than 10 seconds, start over at one. The same method is used during hours of darkness.
As an alternative, since light is so fast, you can simply multiply the seconds you counted by 340 to estimate the distance in meters (340 is approximately the speed of sound in m/s, and light is of the order of magnitude of 10^8 m/s so it will not affect your estimate by a meaningful amount) For example: three seconds times 340 gives you 1020m.
The term snap bang refers to the snap of a rifle round passing near you (the observer) and the bang of the report of the rifle. Since the bullet is moving faster than the speed of sound, we hear the bullet “snapping” overhead first, before actually hearing the “bang” of the bullet being fired from the rifle.
This is very similar to thunder and lightning. Lightning, of course, is moving faster than the speed of sound, at the speed of light (186,000 miles per second or 983,571,058 ft/s). During a thunderstorm, we see the lightning first, then we hear the thunder. When determining how far away a thunderstorm is, we use a simple counting method. Of course, this scale will vary when relating to a bullet and the report of a rifle.
The enemy’s supersonic bullets produce a sonic boom, creating a “crack” sound as they pass by. If the enemy’s bullet speed is known, his range can be estimated by measuring the delay between the bullet’s passing and the sound of the rifle shot, then comparing it to a table of values. This is only effective at distances of up to 450-500 meters; beyond this, the delay continues to increase, and at a rate too small for humans to distinguish accurately. Also, in urban areas, the sound can give inaccurate results due to the fact that the buildings in the area can relay false sound directions.
We will give an enemy’s bullet velocity a solid number of 2,700 fps. In the case of a bullet leaving the muzzle at 2,700 fps (900 yards per second), at 100 yards the bullet has dropped to around 2,500 fps. We can average the velocity over the 100 yards to be approximately 2,600 fps. At 2,600 fps, the 100 yards will be covered in about an eighth of a second—you will not be able to distinguish between snap and bang.
Being that bullets slow down the farther they fly, at around 500 yards, the bullet has a velocity of around 1,800 fps. The space between you (the observer) hearing the snap and then hearing the bang, which is a “constant” (the speed of sound), will be about a second. So if we can distinguish a second or more, we can start to look for a sniper at around 500 yards or more. Anything that is less than a second, but still distinguishable between a snap and bang, should indicate the enemy’s position in an area 200-400 yards away from where the rifle report (bang) was heard.
One-second five count
Another technique a sniper may use to determine another’s sniper location is to use the “one-second five count.” The one-second five count is done by counting to five in one second. This count starts when you hear the snap of the bullet, and stops when you hear the bang. Each number equals that many hundreds of yards: three is 300 yards, four is 400 yards, etc. This technique has been shown to accurately locate the distance of sniper within 30 yards. Please note that this technique, as discussed, is only accurate up to around 500 yards.
Snap-Bang Method Chart (.308 168gr, HPBT Match)
Bullet travel time vs. sound travel time
Distance Bullet/Snap Bang Difference
100 yards .12 .27 .15
200 yards .25 .54 .29
300 yards .39 .81 .42
400 yards .54 1.08 .54
500 yards .70 1.35 .65
The maximum practical distance
600 yards .88 .60 .72
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