Google Tom Roster. I believe he authored a study on that subject. Tom Roster is a renown ballistician, but I disagree with his premise that it takes 1.5 ft-lbs of KE to reliably kill a turkey. Certainly his number is conservative. It works with lead shot, but not so well with some of the newer denser offerings that were not available at the time of the study. The denser materials can penetrate deeper with less KE than lead requires, due to their smaller surface area. And penetration of CNS bone is what kills turkeys, not KE.
