Chiefbob81 it can very well be some of the issues stated.
During the manufacturing process the frames "recievers" are heat treated, beneath the barrel portion of the frame becomes a little more brittle due to how thin it is. Now add a heat, kenetic energy and a slight misaligned cylinder, if you fire a round into the forcing cone again and again where those thin threads are it can and will eventually fail, and as others have stated you absolutly should retire the frame.