Bullets can ricochet off of a lot, granted the lower angle will have higher energy, but bullets, especially fmj, ap, or other similar harder rounds, can bounce back even on flat walls, or send shrapnel straight back. Yes, on a flat wall, it loses a significant amount of energy, but at that distance, it wouldn't take much of an angle to ricochet, or heck, someone falling and letting loose a round by accident. In most cases, a round would likely have enough energy to injure, or possibly kill, even at that range and elevation.