My gongs didn't dimple for years and I usually have a lot of company with rifles .
They have taken most the rounds 556,762x39 and 308, 12g slugs and Buck between 20 to 100 yards, use them for "training " like shooting. "Fast" and not so muched aimed, just enough to make it ring and move to the next one
06,243,270,300 win mag,338 win mag 100 to 200 yards....... Everything beyond that goes on paper because its all about the grouping with scoped high power rifles, my AR and an AR10.
Only 855 that have been put on mine have been a total accident a couple badass X39's hurt them a little too but most good way to ruin expensive targets. My gongs are AR500 done right, water jet and all so another vendor wont make a difference.
Most those dimples are from 55gr FMJ at NATO speed .....just started doing it one day
Just recently hit one with a 308 and broke an ear right off , turned it into a static target and when I hit the broken edge with a big angle grinder I didnt thing it was going to grind it down at first, took an entire disk to grind a 1/4 inch of material....wow