Gary Roberts has published a list of various 5.56 rounds which meet criteria based on what the shooting need is (barrier or not, etc). There are no magic bullets, including .308 or slugs. Some folks are hard to stop, and placement really matters. One can have non-survivable wounds and continue to function - even a few seconds as described early in the string is too long on the 2 way range, but that sort of outcome will not change in the near future.

I'm comfortable with my AR as a patrol rifle, because at close range I can do an NSR (non-standard response) in short time in a reasonably small space.

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NHI, 10-8.