A while back I wrote a bit on the subject of what distance to zero your AR. Just for giggles, here's some more information from Robar on that subject. It's some good stuff, so take the time to read and digest. I'd pay particular attention to the part about the ranges at which you can expect the 5.56 round to be more vs less lethal. That's some handy to have information there. I have an old article I clipped from Shotgun News years ago, this jibes with it 100% on that subject.