system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do the iron sights on a gun work if they are above where the bullets are fired?
gpt
Iron sights form a straight line, while the trajectory of the bullet is an arch (as the bullet falls down during flight). Usually the sights are calibrated in a way so the bullet path intersects twice with the line of sight of the iron sights. The distances where they cross (where you can get an exaxt hit) depend on the weapon and its effectice range. Nearer and farther than these two points you hit low, between them you hit high. The exact measures on how low/high you hit, againm depend on the weapon.

Adjustable scopes can be changed to (almost) always hit perfect. But you have to know the distance to your target or estimate it.