I shot mild plate steel at 15 feet at an angle, what your really saying is that if you don't have any concept of mechanical engineering or physics then don't do it.
If you had a sound knowledge of physics and ballistics, you wouldn't shoot mild steel with an AR, at all. I've done it to test targets, wearing a MICH helmet and body armor, M855 pockmarked AR500 at 25m. Don't do it.
You can shoot cold-roll mild steel with cast bullet 38's and 45acp all day long. When the plate bends you just flip it over. If you shoot it ONCE with an AR, it's got a divot forever, it is then forever unsafe at any distance as a pistol target.
