I don't remember the SPs doing the damage, it was the "blemished" rounds I thunk... or some sort of FMJ round. I remember your softpoint stuff being fine. I do remember you had a FMJ that was not magnetic that still dimpled quite a bit.
Chains do not make a difference, as near as I can tell. Round composition makes a difference, but velocity is the biggest deciding factor.
In the end, everything has a finite life (equipment wise) so just be aware. I am sure the 300WM was not kind to the steel this weekend. That steel was a bit on the cheaper side, but still holds up well.