I know ar500 can not take 5.56 from less than 100 yards repeatedly
it dimples, bends , craters and craters send fragments back at you.

I would like to hear more about this. How thick was the plate, was it swinging or solid, actual distance, and if you was using AP rounds. Also if your steel came from a reputable resource.
I only ask as my experience with the ar500 is totally different, and I am guessing a variable exists.
I now have hanging ar500 gongs of various sizes and a couple spinners at 45, 60, 100, 150, 200, and 300 yards. The ones at 45 have only taken a few hits from 223/556(like a hundred or so from the kids), my 60 yard plates take quite a few rounds from myself and buddies (in the thousands of rounds on the original plate). The 45 yard plate dose have a few dings, not craters just enough of a ding to know a hit was made in that spot. The 60 yard original has the same dings. I would say these dings are same diameter as the dimples on a golf ball and maybe 1/3 the depth of the ball dimples. My plates are all 3/8 or 1/2 inch thickness. The originals are 3/8 and newer ones 1/2 inch thick plates.