Interestingly I have had some "I'm very dead but the rest of my body doesn't realise it", with my .17HMR recently. On head shot rabbit the result of the .17HMR is colossal, but I often get great leaps and twitching from the carcass. I think my .22LR produce more "roll over" with less final twitch. Much must be in the threat flight mode the rabbit is in before being hit. Changes during the year too, so some must be the energy levels in the rabbits. Odd things happen.

I have always thought 12ft/lbs was only just enough and its all in shot placement. For around the farm buildings them 12ft/lbs has an important role. 14 to 18ft/lbs would make "shureness" a little easier, if only for the flatter trajectory. I shoot .177 but if I had a bit more power/velocity then it wouldn't take much for me to switch to .20 or .22. Practice and knowing your combo is what pays off in the end. The more shooting you do, loads on paper, the better; its all shootig so whats not to like