RE: Federal Fusion..NOT impressed
Federal designed that bullet from the base up for white-tail deer and related game (with respect to size and bone density).
Now, since it is a bonded bullet, I would suspect that it would be fine for elk. But, if you jacket and core separation with a bonded bullet, it was likely with a fast moving bullet (like a 7mag) and it was likely inside of 150 yards. It may well have just turned inside out. Did you acctually FIND a separated core and jacket? And you can pop the lead freely in and out of the jacket like you can with a Sierra GameKing?