I have 6 gongs, 5 are 3/8" and one is 1/2". Mine are Hardox 500 but most people say it is close to the same as domestic AR500. All have thousands of rounds fired at them with no cupping or denting whatsoever.
A few years ago I had a 1/4" gong made from Hardox 450 that cupped, dented and pitted. I suspect most of it was from the softer alloy
