In my Royale 500 the regular heavies are grouping better than the MK2's at 60 yards. The heavies fit much more snugly in the barrel than the MK2's. It's very easy to feel the increased resistance when pushing the probe forward. Only shooting both pellets around 775 though, so need to bring that up to about 840 - 850 to get the full benefits of the pellets design. But I imagine, that due to my particular barrel liking the heavies fitting snugly, that at the faster FPS they will still be accurate than the MK2;s.... But, we shall see.