Rabbit hunting: I'm doing this wrong (UPDATE!!!)

So I replaced my 500fps Daisy Powerline 880 with a 1200fps Crosman Optima. Harvested three cottontails last weekend, three head-shots. In all cases the Pellet went clean through the critter's skull. A very nice gun for the price, scope is ...okay, and a bit heavy at almost 7 lbs. But I like it!! Many thanks to all of you on this forum who have shared their experience.