I've been shooting the X since 1989 and I have never seen that an X fail to make it to the vitals!
I have lost pedals, but never all of them before the vitals.
I have lost all the pedals, but only after smashing both shoulders.
Elk, moose, grizzly, bison, kudu, cape buffalo, hippo, giraffe, zebra, water buffalo down to as small as dik-dik...you name it and I've put its lights out and gotten expansion with with a 270 or 300X.
Some of the early bullets wouldn't expand at all, but that is ancient history.
What bullet weight were you running?