A couple of years ago, someone near us (at a very popular informal "range") decided to try shooting clay pigeons with an AR. There was a hill that, theoretically, should have served as a backstop, but they kept gradually throwing the clays higher and more vertical to the point that they were easily clearing the hill and probably well into the not-so-sparse farmhouses on the other side. My son and I packed up our stuff as fast as we could and beat a hasty retreat. We were met on our way down the mountain by a couple of sheriff deputies and we pointed out where the idiots were. I don't know what the outcome was and I'm glad we didn't stick around to find out.
I have an uncle who used to be able to hit them about 80% of the time with a 22, but we were in an area where we could see close to 15 miles of bare salt flat in the direction we were shooting. Not much of a backstop, but there's no way that anyone was anywhere near enough to get hit. Not even coyotes or jackrabbits (unfortunately).
Matt