Question: How does the sound power decrease with distance"? Answer: "April fool - The sound power does not decrease (drop) with distance from the sound source."
Levels of sound pressure and levels of sound intensity decrease equally with the distance from the sound source. Sound power or sound power level has nothing (!) to do with the distance from the sound source.
Thinking helps: A 100 watt light bulb has in 1 m and in 10 m distance really always the same 100 watts, which is emitted from the lamp all the time. Watts don't change with distance.
A frequent question: "Does the sound power depend on distance?" The clear answer is: "No, not really."
Based upon the above, I'm firing a 308 with a 24 inch barrel, the 24 inch distance doesn't really matter.
For your rifles, the major sound impulse is going mostly forward and to the sides, not back at you.
Also, energy drops 6dB for every doubling of distance, whether it is light or sound. Spherical expansion of the energy, impossible for it to remain the same intensity if you stop and think about it.
Someone should ask the genius that wrote this, "Why can't I use a 100W bulb to read 100 feet away if as you imply, it is just as bright?"
Doesn't make sense. I can hear people shooting shotguns in fields that surround my area but I don't need ear protection.
The are arguing semantics. Being further away from the gun does not make the gun quieter, it is just as loud, but the energy delivered to your ear drops by square of the distance. Distance is very important, otherwise all that shooting in the middle east would have deafened all of us by now.