It takes a solid hit to the nervous system to put down a turkey on the spot. That means that one, or hopefully many more, pellets has to hit the brain and/or spinal column with enough energy to destroy it.
Many hunters forget to pattern their shotguns, decreasing their chances of dropping a bird. Turkey hunters should spend time on the range shooting at turkey targets and evaluating the patterns to find a turkey load that consistently places several pellets in the nervous system of a turkey.
Every time you change your choke tube, shotshell brand, go from led shot to extra dense, or change pellet size or sighting system, the pattern will most certainly change.