In the case I saw, the rifle was a CMMG, and the owner had been shooting Wolf exclusively for "about thirty boxes."
I'm not sure the steel-on-steel contact was the only cause, as the bolt face was encrusted with a level of scrunge I can only describe as "epic." I'd hazard a guess that it was a combination of the two, but I've never seen it on a rifle fed brass-cased ammunition.
It sounds like the primer sealant they used to use. It gunked the bolt face up particularly under the extractor which caused failures to extract especially if the chamber is badly carbon fouled as well.
Over the last few months they've stopped using the sealant because of customer complaints about it.
Don't get me wrong guys; I'm not saying there isn't better ammo out there. There obviously is better ammo; I just don't see a need to run premium ammo for training where I'm running through a case or more in two days. I'm just saying that the things it gets blamed for aren't possible from a logical or metallurgical standpoint.