Sorry to hear that story. But this is exactly what I need to hear. It is hard to find a good bullet for little cost that performs well. I used the Speer 300 grain Gold Dot bullet for years until I couldn't find them any longer. I had 1 issue with that bullet. Shot a large mule deer on a LE unit. Deer dropped like he was hit with a sledgehammer. Got up and wandered off. He was about 70 yards when I shot. Entry hole bled very little but no blood on the exit side. Tracked it for couple of days but no sign. Turns out some other hunters found him dead and took him. I found the carcass in their camp a few days later. It was a good hit but the bullet did not exit the body, just broke ribs on the exit side under the shoulder. These bullets are very similar to the XTP and always performed well on small to medium size deer. Sometimes I think these odd things happen. With the thick jacket and plastic tip I can see where the PTX bullets may perform as you said.
Maybe I can shoot these into something (any ideas what) to get an idea of performance. I just don't want wounded animals. Thanks for sharing your story, again I am sorry for the loss of your elk.