turkey zero
A shotgun pattern is such a fickle thing that worrying about "drop" is pointless.
Your working with a cloud of shot varying in size (expanding) depending on distance from target to muzzle. Drop at small pellet range for gobblers is nothing to worry about.
My drill for zeroing a gobbler gun is to shoot at 20 yds from a solid bench, much as one would zero a rifle. Use standard field or game loads and shoot at a high visiblity aiming point (2"?) on a 24" or so clean backer. At that distance, the shot cloud will yield a pattern maybe volleyball size, 9-12". Adjust sights/sight system to land this small pattern as best centered as possible around the aiming point. A good combo may well obliterate the center.
I then back off to 30yds, and shoot a benched turkey load to see if all is well, and adjust as necessary, but often is not. At 30 yds my guns and loads will shoot basketball sized patterns. I will occassionally shoot to 40 yds, but by then beach ball sized patterns make interpretation a bit of guess work.