1Akshooter,
Ross and I discussed the original X-Bullets at length, including the results on Australian feral donkeys. Two things might be pertinent here: Ross mostly shot for shoulder-bone, often on quartering-to shots, which is where they really impressed him.
The early X's also tended to shed their petals, so did more internal damage. I know this from a conversation with Randy Brooks on a mule deer hunt in, as I recall, 2003. He thought that was a good attribute, since it didn't affect their deep penetration, but he thought it did help them kill quicker. But so many customers saw petal loss as negative, apparently because it involved less-than-100% weight retention, that like any good business person he decided to please his customers, so modified X-Bullets until they usually retained their petals.
Personally, in shooting various X-Bullets into big game, from the originals to the TTSX's, and seeing other people kill animals with 'em, I've also never been able to see any difference in whether bullets that retained their petals killed better or penetrated deeper than bullets that didn't. This may be due to recovered X's often being shot through bone, which does tend to break petals off--and also reduces the frontal area, which enhances penetration.
From what I understand, some more recent X's are again designed to not retain the petals, a by-product of being designed to open up at longer ranges.
