I have used the .458 X for several years. I use the load recommended in the contender loading manual. It has never failed to put down a deer instantly. I can't tell you about the performance of the bullet because I have never recovered one(5 - 120yds). From the size of the exit hole, it must not expand much. It does appear to be larger, but not much. I don't think any of the deer knew that it did not expand.