Brad, two thoughts: First, yes, I would recommend lead pellets. I've never found any other alloy that shoots as well in my rifles, but I haven't really done much experimenting. Second, like many folks, I generally shoot squirrels in the head, largely as a matter of pride I guess. But, since I have killed so many in my pesting capacity, I have had the opportunity to experiment with various shot placements. Much to my surprise, a shot in the heart/lung area has proven equally as effective as the brain. I can't explain it, as that was not my experience growing up squirrel hunting with a .22 RF. My only thought, with the lower velocity and lighter weight of the pellet, maybe it expends so much more of its energy in the target, that its lethality is increased, just a guess. But regardless, I'm convinced of the results, as I've killed a bunch of squirrels using that hold, and they generally drop on the spot. My point, it's a larger target with a greater margin of error, and my experience suggests it is just as humane.
Ed