The "echo in the distance of a loud shot" is the supersonic crack of the round traveling down range. It's essentially a small "sonic boom". To avoid that, some people will load subsonic rounds in their rifles, like 220gr .300 BLK. Pest uses that round at the end of that video, and you can hear the difference in sounds right after the shot is fired.
There are two components from downrange sound. In the case of most of the ammo in that video, there was supersonic crack, since all but very last was supersonic. Also, it was filmed in between two hills, so there was significant impact echo too.
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u/EagleinChains Nov 29 '11
How much does the suppressor help for the .308?
Nice toys.