Out of my neither of my two Crown MK2 nor my MK1 using 600mm pellet A, 600mm Superior, 600mm Superior Heavy, 380mm pellet A, or 380mm Superior liners, I have had absolutely NO luck in achieving anything consistently accurate at 100 yards using .25 King Heavy or .25 King Heavy MK2 at any of the slower speeds(that Ted reportedly shot the King Heavy thru his Impact with to win EBR) that are "supposed to be a sweetspot". I can always see them start spiraling at 75 - 100 yards until I get the speed up over 900 fps to stabilize them(I notice this same phenomenon when shooting .22 MRDs, .177 Monsters and any other non-small waisted pellets). They are all fairly stable and accurate at slower speed at closer distances, but I have to get the fps up to stabilize them and keep them from spiraling at farther distances.
This is just my verified experimentation with the equipment listed. Your milage may vary.