I have only used JSB .25 kings at 850 fps. At a target range of 25 yards I have never got a pass through on head shots on raccoons, opossums, or even a body shot on a crow. No problem dropping a 28 lbs coon with kings to the head. All were DRT except for 2 raccoons which I'm pretty sure were nailed 3/4 - 1" above and between the eyes. No body or blood found. My guess is that the pellet bounced on the skull. It is hard to tell at night if the raccoon's head is looking up or towards you, or angled down. Unless the head is angled down the slope presented by the skull increase the chance of a non-penetration. I have read stories of even a 22LR bouncing off of a raccoon's head. My most recent shot, 2 raccoons were present, a smaller one presenting a side profile and a large one facing head on. I took the smaller one not to chance the pellet failing to penetrate the skull. BTW that same JSB kings work well on a lung shot on a raccoon but it walked off over 70'. Never found the body in the morning, only a blood trail leading up to a puddle of blood about 12" in diameter. Some other animal must of took it for dinner.
I do agree that first and foremost accuracy is needed , but only to the point that you can hit what you are aiming at. I'm open to any suggestions as to what type of pellets that would work best for a head on shot on raccoons. Currently I'm reluctant to take that kind of shot because of 2 failures. I have yet to try MK2 heavies, but is practiced with H&N barracudas, Crosman premiers and polymags that all group well enough to hit better than .75" at 25 yards. I don't know if they would be better than the JSB kings.