Any real gun person would know that a 556 at close distance kills metal targets which in turn either destroys them (expensive) or makes them likely to rebound shots.... I imagine at about 500 yards the lead has slowed down enough to not damage the target (if thick enough 1/2 hardened 500 metal), but at that distance (at the photo op just a few feet) it is very dangerous (and stupid). I would expect the zombie liberal reporter to not understand the dangers, but anyone in the military should of known better.
One viewing of a tracer round exploding in all directions when hitting a metal target would show one that being anywhere near a metal target is crazy. One always has some risk involved in shooting metal, but most folks accept that danger and shoot distant metal at long distances with a 556/223... and can shoot smaller handgun ammo at closer ranges (50 to 100 yards)... any closer even with handguns (9mm, 380, 38 special) there is a risk at 50-100 yards, but most shooter still do it accepting the risk.
TLDR: Shooting a AR-15 556 at close range is stupid (and destructive to targets that are expensive to replace). Metal targets at close range are usually reserved for only pistol calibers, not 556/223.