How to Zero a Red Dot Sight: 25, 50, and 100 Yard Zeros Explained

A zero is a distance, not a setting. When someone says a rifle is zeroed at 50 yards, they mean the bullet crosses the line of sight at 50 yards. Everywhere else, the bullet is either above or below where the dot is pointing, and how far off depends on how far away the target is.

That one idea explains every zeroing argument you have ever read. Here is how to use it.

Why the bullet crosses your line of sight twice

Your optic sits above the bore. On a typical AR-15 with a micro dot, that gap is somewhere around 2.6 inches. The barrel is therefore angled very slightly upward relative to what you are looking at, so the bullet starts below the line of sight, climbs through it, arcs over the top, and falls back through it again further out.

Which means every zero has two crossings:

• The near zero. The first crossing, close in, where the rising bullet meets the line of sight.
• The far zero. The second crossing, further out, where the falling bullet meets it again.

Between the two crossings the bullet is above the dot. Past the far zero it drops away fast. Picking a zero is really picking where you want those two crossings to land.

The 50 yard zero

The most common choice on a general purpose carbine, and the one we would recommend to most people. Zero at 50 yards and, with common 5.56 loads, the bullet comes back down through the line of sight somewhere around 200 yards. Between those two points it never rises much more than about two inches above the dot.

Practically, that means from the muzzle out to roughly 200 yards you can put the dot where you want the hit and be within a couple of inches. On a torso sized target that is a hit every time, with no holdover to remember. It is the flattest, simplest thing you can do with a red dot.

The 36 yard zero

Zero closer, at roughly 36 yards, and the far crossing pushes out to around 300 yards. The tradeoff is that the bullet rides higher in the middle of that span, peaking at roughly four inches above the dot around the 150 to 200 yard mark.

This is the classic carbine battlesight zero. It buys reach at the cost of precision in the middle distances. If your shooting is mostly under 200 yards, the 50 yard zero is the better tool. If you want the widest useful span on a target you can afford to hit high, the 36 yard zero has a real argument.

The 25 yard zero

Zeroing at 25 yards is mostly a practical decision rather than a ballistic one. A lot of indoor ranges are 25 yards, and 25 is close enough that you can see your holes without a spotting scope.

Two things to know. First, a true 25 yard zero on a 5.56 carbine tends to put the far crossing out near 300 yards, with the bullet riding high in between, similar in shape to the 36 yard zero. Second, at 25 yards a small error in your point of impact becomes a large error at distance, because the angle you are correcting is tiny. A quarter inch off at 25 yards is roughly an inch off at 100.

So use 25 yards as a place to get on paper, then confirm at 50 or 100 if you have the room. Never treat a 25 yard group as a finished zero if you intend to shoot past a hundred.

The 100 yard zero

Simple, honest, and easy to think about: the dot is the hit at 100, and everything closer is a little low. It is the standard for precision rifles and it works fine on a carbine, but it costs you the flat span that makes a 50 yard zero so easy to use up close. On a red dot carbine it is usually the wrong tool.

How to actually do it, in about twenty rounds

1. Check the mount before you shoot. Every screw on the optic and the mount, to the manufacturer torque spec, with a torque wrench. If the mount moves, nothing else on this list matters. See mounts.
2. Set up at 25 yards to get on paper. A big target and a clean backer. You want to find your holes, not hunt for them.
3. Shoot a group of three from a stable position. Bags, a bipod, a bench, anything that removes you from the equation. Three rounds, not one. One round tells you nothing.
4. Measure from the center of the group to the bullseye. Not from your best shot. From the center of the group.
5. Do the adjustment math once. Most red dots adjust in 1 MOA or 0.5 MOA clicks. One MOA is roughly one inch at 100 yards, so at 25 yards it is roughly a quarter inch, and you need about four times as many clicks as you would at 100. Count them out loud.
6. Move to your real zero distance and confirm. Fifty yards for most carbines. Shoot another group of three, adjust once, and shoot a final group to confirm.
7. Write it down. Load, bullet weight, distance, and the date, somewhere you will find it again. A zero belongs to a specific load.

Where people go wrong

• Chasing single shots. Adjusting after every round walks you around the target forever. Groups, then adjust.
• Zeroing with one load and shooting another. A 55 grain and a 77 grain load do not share a trajectory. Zero with what you will actually shoot.
• Ignoring the mount. A group that opens up over the course of a session is usually loose hardware, not bad ammunition.
• Forgetting the dot is not the bore. At contact distance your rounds land roughly two and a half inches below the dot, because that is how far the optic sits above the barrel. Inside about ten yards, hold high.
• Not confirming after a change. Removing the optic, changing the mount, or swapping the handguard means you confirm the zero again. Quick detach mounts usually return close, but close is not confirmed.

Next steps

Still deciding between a dot and magnification? Read red dot vs LPVO. Shopping for the optic itself, or for the mount that holds it, start with optics and mounts.

And if you would rather have someone walk you through a zero on a live range instead of reading about it, that is one of the things our lessons cover, in person or over video.