[masraum]

I don't have any experience. My grandfather used to keep the squirrels out of his pecan tree with a pellet gun, but I wasn't around enough to know what to expect.

Yes, there are folks that consider squirrels to be "rats with fluffy tails" (not my grandfather, he just didn't want them eating his nuts).

I have to think that the immediate kills are based to destruction of the brain/spine. I believe the only way to immediately kill something is by destroying the brain (probably especially the part closest to the spine and/or severing the spine near the brain.

I think to confirm that with evidence would require necropsy which I don't imagine happens much.