Kings vs Kings Heavy MKII in my Vulcan Tactic 6.35

Today i tested JSB Kings vs Kings Heavy MKII in my Vulcan Tactic with the new synthetic stock.
Distance 75y. Very slight wind.
Kings 880 fps
MKII 790 fps.
The MKII has better BC but clearly the groups with Kings are better. I assume it’s because MKII’s do not get adequate speed.
It would be interesting to see MKII at 860-880 fps but the Vulcan does’t have enough power for that.

My rifle

MKII 75y

Kings 75y