I have head and read the reports regarding forcing cone erosion an LilGun. That I can understand.

What I can't quite wrap my head around is what is the issue with the 260gr XTP? Why would say the XTP be problematic but the XTP mag would not be?

Regarding the hardness, I was under the impression the difference between the XTP and the mag version was in jacket thickness and the skiving on the nose to make the mag version require a higher velocity to begin to open. I wouldn't think that would cause any changes in what occurs before the bullet leaves the barrel.