Q. Won't JSP and JHP rounds be safer indoors? Don't I have to worry about FMJ rounds going through walls and hurting my family or others?
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.
Fact: Evidence increasingly shows that 5.56 FMJ rounds like M193 and M855 are not the over-penetration risk they have often been though of as. In interior wall tests, 5.56 rounds have less wounding potential after wall strikes than any common 9mm or above handgun ammunition and/or 00 Buck shotgun loads.