As is usual for me, I'm sitting at my desk, minding my own business, when BAM! something hits the roof of the work trailer I'm in ... hard. It was really loud. Then we hear whatever it is bounce around and fall off the side.
Wtf? Sit still for while, to see if there's anything more coming. Nothing. So go outside and start looking around. We figure it was a stray bullet. One of the local guards is looking around, he heard the gun fire then heard it hit the trailer and he thinks it's a stray bullet too. I even stood up on the sandbags to look on the roof, er, with my Kevlar helmet on, looking for it. No luck.
I spent some time playing Physics 101, and a little web research, and figured that a rifle bullet shot straight up (with a muzzle velocity of 2000-3000 fps) comes down at only a few hundred fps (due to wind resistance), it might be going faster in a shallower arc but it's still much slowed by the time it's lobbed over the walls of the camp, given the height of our walls, and a rifle bullet is light compared to a handgun bullet ... so the short story is that I think our roof is "bullet proof" (when the bullets are lobbed, not from direct fire) and I think that was empirically demonstrated too.
...oh goodie...