How to zero AR-15 iron sights
Quick answer: set a mechanical zero first (rear windage centered, front post at base height), then zero at 25 yards for the classic 25/300 battlesight zero or 50 yards. Fire a 3 to 5 shot group and adjust to the group: the front post sets elevation and the rear sight sets windage. The rule is FORS, Front Opposite, Rear Same, so turn the front post down to raise impact, and move the rear sight the same way you want the bullet to go.
A plain-language guide to zeroing AR-15 iron sights, and remembering which sight moves which way.
Iron sights zero on the same principle as any sight, adjust until point of aim equals point of impact, but the controls are split in a way that trips people up: elevation lives on the front sight, windage on the rear, and the front sight moves opposite to the bullet. Get that straight and the rest is a few groups from a rest.
Steps
- Set a mechanical zero first. Start from a known baseline. Center the rear sight windage so it sits in the middle of its travel, and set the front sight post to its base height (on a standard AR-15, screw the post down until the base is flush, then raise it the number of clicks your manual specifies). A mechanical zero puts you close before the first shot and gives you equal room to adjust in every direction.
- Pick your zero distance. For an AR-15 in 5.56, the classic choice is a 25-yard zero, because it also puts the bullet back on target near 300 yards, the improved battlesight zero. A 50-yard zero is the other common option and returns near 200 yards. Set your target at the distance you chose and shoot from a steady rest so the rifle, not your hold, is what you are testing.
- Adjust the front post for elevation. Fire a slow 3 to 5 shot group, then move the point of impact up or down using the FRONT sight post. The rule is counterintuitive: move the front sight the OPPOSITE way you want the bullet to go. To raise the point of impact, turn the post down; to lower it, turn the post up. Adjust to the center of the group, not to a single shot, and check your sight manual for its click value.
- Adjust the rear sight for windage. Correct left and right using the REAR sight, and here the rule flips: move the rear sight the SAME way you want the bullet to go. Rear sight right moves impact right. The whole memory aid is FORS, Front Opposite, Rear Same. Make the windage correction, then fire another group to confirm both axes are on.
- Confirm and understand your zero. Fire a final group to confirm the sights hold, and make one small correction if needed. Remember what your zero means downrange: a 25-yard zero is also roughly on at 300 yards but prints high in between, while a 50-yard zero is near on again at 200. Confirm at a longer distance if you can, and record your final front-post height so you can return to it.
Common mistakes
- Chasing single shots. Adjust to the center of a group, not to your best or worst round, or you will dial back and forth forever.
- Forgetting FORS. The front sight moves opposite the bullet; the rear moves the same way. Reverse them and every correction doubles your error.
- Skipping the mechanical zero. Start centered, or you can run out of adjustment travel on one side mid-zero.
- Not confirming downrange. A 25-yard zero prints high at mid range; know what your chosen zero does at the distances you actually shoot.
FAQ
At what distance should you zero AR-15 iron sights?
The two standard choices are 25 yards and 50 yards. A 25-yard zero is the classic military improved battlesight zero because the bullet crosses the line of sight again near 300 yards, giving a usable close-to-long hold with one setting. A 50-yard zero returns near 200 yards and keeps the mid-range trajectory a little flatter. Either works; pick the one that matches the distances you actually shoot, and confirm it there.
Which iron sight adjusts elevation, the front or the rear?
On a standard AR-15, the FRONT sight post adjusts elevation (up and down) and the REAR sight adjusts windage (left and right). The memory aid is FORS: Front Opposite, Rear Same. Move the front sight the opposite direction you want the bullet to move, so turn the post down to raise your point of impact. Move the rear sight the same direction you want the bullet to move, so rear sight right pushes impact right.
What is a mechanical zero?
A mechanical zero is a known starting position for your sights before you fire: the rear windage centered in its travel and the front post set to its base height. It is not a firing zero, but it puts you close to the target on your first group and leaves equal adjustment room in every direction. Setting it first is what keeps you from running out of travel halfway through zeroing.
Can you zero iron sights that co-witness with a red dot?
Yes, and you zero them independently. Zero the iron sights on their own first, then mount and zero the red dot; when both are on at the same distance they will co-witness, meaning the dot sits on or near the front post in the optic window. Confirm the agreement on paper rather than assuming it from sight heights. If you run backup iron sights under a dot, see our best backup iron sights picks and our red dot vs iron sights guide.
Setting up a backup set? See our best backup iron sights picks and offset iron sights guide. Deciding between irons and a dot? Read red dot vs iron sights. Zeroing a dot or a scope instead? See how to sight in a red dot sight and how to sight in a rifle scope.