I have had the same experience, I tried the original X bullets in 6 MM and 30 cal. and they didn't group well and showed pressure signs before I got near max loads.
In the past few years have killed game with the 270, 7 MM, & 30 cal. TTX bullets and a antelope with a .357 XPB bullet and have had nothing short of perfect game dropping performance and they shoot like match bullets now. Jed