While size is a factor, pattern density is what you should be concerned about. A good turkey choke will concentrate the pellets in the center of the pattern. The pellets at the edge of the pattern may be a thinner density, but they wizzed past his head anyway. Most guys use a turkey head target rather than a pattern board to check their patterns for this reason. You could probably shoot hevi-shot through your x-full choke. The x-full factory choke for my BPS mic's at .670. But you may get better patterns from a tube which is designed to shoot hevi-shot.