Yeah, um that would make me VERY unhappy! I don't see any polishing indicating a crack so it looks like a catastrophic failure. I believe the manufacturer should be getting a call demanding a replacement. Hope you haven't made any modifications or were shooting a hot load...
This is a fairly high stress area during recoil if the spring is not the proper weight. This problem is not unlike what plagued the Baretta 9mm when it was first adopted by the military.
Those fractographs are considerably better than what most of my clients present.
Notice the darker appearance of the fracture surface at the bottom corners of the fracture. This is a good indicator of an older fracture surface relative to the rest of the surface. I do see what appears to be a small area of high-cycle fatigue at the bottom corner of the last photo. No big surprise - that corner is sharp and a good stress riser. Couldn't the manufacturer machine a more generous fillet there?
