Generally my primary " aiming point" is exactly as the others describe--junction of red neck with feathered body. (Unless the turkey is less than ten yards away, when I [wrongly, I suppose] tend to aim a tad more directly at the head, due to the constricted pattern.) Also, as noted, pattern your gun with the shells you' ll be using in the field. Know your gun' s aimpoint, know the pellet distribution/pattern at various yardages. Know if your gun has any " drop" at 40 yards that would require you to adjust your aimpoint.

Then have fun this spring!!