Quote:
Originally Posted by Skybird
I assume that more or less the bullet travelled near the speed of sound. 3.5 kilometers, 10 seconds flight time: average speed 350 m/sec. Speed of sound: roughly 340 m/sec. The shot sound probably arrived at the target area 0.5 seconds after the target was hit, plus minus some tenths of a second.
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The .50 BMG round is listed as traveling at 1200 m/s (EDIT: thats for the browning machine gun from WWI, the M107 Sniper rifle uses a .50 round that travels at 853 m/s), but there would be substantial losses in that velocity over the distance traveled resulting in the ten second flight time. Plus, I'm not sure if they were actually timing the shot to the tenth of a second, so I'd guess 10 seconds is just an estimate.
But regardless of the math, the bullet was supersonic initially, leading to it arriving long (relatively speaking) before the sound did.
But while the bullet travels in a "straight" (ignore ballistics) line, the sound travels in every direction. It is governed by the inverse square law. Where if you double the distance, the energy of the wave is now 1/4. Quadruple the distance, and it's 1/16 the energy. By the time it reached the target, it would have been barely noticeable. Especially in a location that distant gunshots are not uncommon, it probably wouldn't even have been noticed.