A while back, I wrote a short article stressing the importance of actually focusing on the front sight when using iron sights. One commenter, whom I wish to personally thank, noted that I had not explained why doing so is important. Looking back, it was a critical omission that is important to correct.
Three things make focusing on the front sight a critical part of marksmanship: the geometry of sight alignment, the human eye’s depth of field and what wiggles the most on a firearm. Let’s start with geometry.
The barrel of the firearm points along the same horizontal axis as a line that joins the center of the rear sight with the center of the front sight, if the sights are adjusted properly. Seen from above or below, the bullet’s path and that line (the line of sight) are one line if there is no horizontal force like wind to pull the bullet away. (There are miniscule variations to this that are significant only for precision shooting.) That means that if the sights aren’t aligned on the target, the bullet will miss what the shooter intends to hit. The more they are misaligned, the farther the bullet strike will be from the target. So if your sights are 1 foot apart, a 1/12-inch error at the front sight will multiply to 90/12 or 7.5 inches at 90 feet. You don’t want to be 7.5 inches off at 30 yards.