Terry I had a Nosler Partition do that on finishing shot on of our crew bull elk a few years ago. The bullet didn't pentrate through the neck either and was in pieces with only a small part of the shank found. I attributed it to PB range and MV being high, certainly the NP has worked for me and countless others on big game animals so I wouldn't say it was failure.

Quick questions for you, as now I am curious. On the first shot where did you find your bullet? What did it look like in retention and expansion? Did it break bone(spine) or deflect in your opinion? Since I never encounter any heavy bone just thick hides on both my animals, I am curious if you felt it would work on busting into heavy shoulder shot if it arose or the NP's would be the better choice on the likes of Moose and Elk!