You always have to worry about it, of course, but even FMJ 5.56 rounds will have less wound potential after penetrating a wall than even 9mm handgun rounds. Generally after passing through an interior wall or two, 5.56 bullets will have lost enough velocity that resulting wound damage would be greatly diminished. It should be noted, however, that all of the above bullets are still potentially deadly to those on the other side of a wall, so plan accordingly. Interior walls are concealment, NOT cover.
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