Ask anyone who's shot rifles and pistols for a while about how to aim with iron sights and you're bound to get different answers. I guess I'm no different. I have my own opinion too.
Many bullseye shooters will tell you to align the top of the front sight with the top of the rear sight and center the front post within the notch of the rear sight. So far, so good. Where we differ is this: Those same shooters will tell you to align the bottom of the bullseye with the front sight so that it looks like a pumpkin on a fence post.
I suppose that's ok if your gun is sighted in to shoot the same size bullseye at the same distance all the time. But what would happen if your gun is sighted in for a 6-inch bull at 20 yards, and then you switch to a 12-inch bull also at 20 yards? Well, if you continue to aim EXACTLY the same way you did with the 6-inch bull, you'll miss the center of the 12-inch bull on every shot. The point of aim is the same, and the point of impact (in relation to point of aim) is the same, but the center of the target has been moved up. Also consider how you would aim those sights on a tin can or small game animal at the same distance? How will you hold "low" on the target so as to hit the target's center?
What I have always done with my guns is to sight them in so
that the point of aim is the same as the point of impact. With that in mind, if
you then align the front and rear sights as before, but hold the top of the
sight on the CENTER of the bullseye, then it doesn't matter what size the
target is because the sights are always aligned on the center of the target.
This method also works well in hunting situations: aim directly on the center
of the animal's head or vitals. Always aim for the center of target
The following diagram shows the relationship between point of aim and point of impact.