Regardless the type of firearm used or the model of the sight on it, that sight must be adjusted. It must point to the spot where the bullet is intended to strike when the trigger is squeezed. The procedure to accomplish that alignment is called “zeroing.” Because there are a few issues to consider during the zeroing of any weapon, we will examine those in an order that might make some sense.
Physics Class
Before we can start, we must understand that a bullet, fired from any firearm, does not travel in a straight line. Instead, it travels through space in a symmetrical open plane curve called a parabola. It will also drift laterally because of atmospheric influence and spin. To further complicate things, the line of sight is straight. Therefore, the parabola needs to be brought into alignment with the line of sight, both laterally and horizontally.
Due to the law of physics governing the flight of projectiles, if a bullet strikes the exact point of aim at 50 yards, it may not hit the point of aim at 100 or 200 yards (assuming the sights have not yet been adjusted for elevation and windage). Because of that, when claiming that a firearm is zeroed, we must specify the distances at which the sights are zeroed.
Yes, I said distances. Because the projectile will cross the line of sight twice during its flight, it is said to be zeroed at both distances. That said, most use only the farthest distance when discussing zero. Beyond that, consideration must be given to the type of firearm. Different firearms are designed to have different effective ranges. The zeroing distance depends on the type of weapon and the ranges at which it is expected to be used.
Typical examples might be pistols for defensive use that may be zeroed at 15 or 25 yards even though most pistols can be fired at greater distances. An AR-type rifle that is typically zeroed at 100–200 yards can shoot well beyond 300 yards. Typically, the zeroing distance for any firearm is the distance at which it is expected to be used under most normal circumstances.
Other Considerations
An important consideration must be given to the manufacturer or brand of ammunition one chooses to fire. Different brands may make or use propellants that produce different amounts of energy. The profiles and weights of the bullets will also be slightly different from manufacturer to manufacturer.
All these variables affect the flight and path of the bullet. It is for these exact reasons that when the firearm is zeroed, it should be zeroed with the type and brand of ammunition that it is to be used with. When any item is substituted, the firearm must be re-zeroed with the new component, or it may not perform as expected.
Another important, but overlooked, issue that affects where the bullet strikes is based on the person doing the shooting and the angle that he/she holds their head. Likewise, how they see the sights when aiming the weapon is another variable. As an example, many rifle shooters place their head so the tip of their nose barely touches the rifle stock.
Considering that different people have different shaped heads, it follows that a weapon which has been zeroed by one person will not be zeroed to the same point when another person is aiming the weapon, especially when metallic sights are used. This is not as problematic with optical sights. However, a good rule of thumb is to never let anyone else zero your firearms — except for a rough zero to get you in the ballpark or more precisely, “on paper.”
Another area of consideration must be the condition or wear and tear of the firearm, it may shoot differently after some use, due to wear of the rifling, chamber, etc. Rough usage may also misalign the sights. Hence, all weapons may need to have their zero checked and readjusted after some use. Additionally, with rifles used for accurate shot placement, the zero needs to be reconfirmed and possibly adjusted when changes in altitude or temperature take place.
With that said, I will explain a procedure to zero basic adjustable iron sights on a handgun and a commercial AR-type of rifle. The same basic principles can be used for zeroing any type of pistol or rifle with any basic type of sight.
As a point of information: The U.S. Army and U.S. Marine Corps advocate the reference distance for zeroing the rifle to be 300 meters. However, the actual procedure is done at 25 meters. To accomplish that, they use a target that has everything scaled by 1/12 actual size. This is also a procedure that you can use to get everything aligned and true before moving to 100 yards or farther for rifles to confirm their zero at actual distance.
It must be remembered that with military rifles the rear sights are adjusted in discrete incremental amounts. Each time they are adjusted by one increment, a clicking sound is heard. Hence the expression for adjusting sights by a specific number of clicks. It must be noted that on some M16 and AR-style rifles, the front sight is also adjustable for elevation.
Mechanical Zero
Before you start the sight-in process with any firearm, you want to establish and set the firearm to its ‘mechanical zero.’ This is accomplished by adjusting the windage knob, so the windage indicator is centered on the windage scale and the elevation knob is set at 100. The procedure will vary for different types of sights. Refer to your firearms user manual for instructions on how to accomplish this with your specific firearm.
New optical sights normally ship from the factory set at their mechanical zero. It is assumed for the purposes of this article that the reader either knows how to correctly install or mount their chosen sighting system or has engaged the services of a competent gunsmith to properly complete the procedure.
Zeroing Process
The next step is to take the firearm to the range and placed it on a firm base, such as a solid shooting bench with sandbags or appropriate pistol or rifle rests that reduces human error. At this point it is important to know the correct point blank distance for the gun and ammunition combination you will be shooting. Point blank is that distance where the projectile crosses the line of sight. It will do that twice but you must know the first or closest distance that will occur so you can set the target at that distance. (For reference, please see the provided illustration.)
To determine the point blank distance, you must know the trajectory of your load. Point blank distance can be computed with a ballistic calculator to get approximate distances (once you know your muzzle velocity). Of course, everything must be confirmed by shooting at actual distances.
With a rifle, you can determine the maximum effective range and it will give you the point blank distances. Pick the first point of intersection as the one to set your target at. For a defensive handgun 25 yards is considered the standard, but you can use 15 yards if you are more comfortable shooting at that distance. For rifles with optical sights, it’s imperative for you to know the exact height of the sights above the bore to compute the point blank distance. It can work out to be anything from 24–50 yards for most normal platforms and loads.
For illustrative purposes, let us look at a handgun to be used defensively first. Once everything is set up, make some notes to keep track the details. I keep a notebook and record the date, firearm, load, distance, temperature, lighting conditions, and wind speed and direction. From a solid rest, I fire as precisely as I can — three slow shots. (Normally I would fire five shots to eliminate operator error but during this time of ammunition shortages and high prices three will do.)
I will note the distance off the point of aim, the order of hits, and size of the group. I triangulate to determine the center of the group and then adjust the sights to a determined number of clicks. This adjusts the point of impact to the point of aim. I let the firearm cool until the barrel is cold to the touch. Then, I repeat the process until the point of aim and point of impact coincide before I call it done.
Final Thoughts
Always remember, accuracy is affected by temperature, altitude, vibration, shock, rough usage (i.e., the sights get knocked out of alignment), barrel cleanliness, etc. It’s necessary to check and re-zero the weapon periodically or whenever a change takes place. How often this is done depends on the user and how much accuracy you expect from each particular firearm. For example, defensive pistols have different requirements on how often to recheck zero than rifles expected to hit prairie dogs at 1,000 yards.
As the Colonel used to say, “Ride hard, shoot straight, and speak the truth!”
How do you zero your sights? Let us know in the Comment section.
Adjustment screws will all have hash marks indicating the amount of movement. Keep track and return to a previous setting if needed.Adjustment screws will all have hash marks indicating the amount of movement. Keep track and return to a previous setting if needed. This young lady is confirming zero off a rest by shooting at a known distance with her .22 pistol. This illustration provides a graphic example of line of sight, bore axis, and trajectory, so the meaning of ‘point blank’ can be understood. Be sure to verify your tools fit the slots properly to prevent ruining their heads. With optics of any kind be sure to confirm the distance that each click will move the point of impact at a given distance, so you don’t chase holes around the target. 
A student confirming zero at 100 yards before moving to 200 and 300 yards (his personal maximum distance for accurate shot placement). 
A class of students on the firing line zeroing their individual rifles using iron, optical, or holographic sights.
This is one article is will be considered required reading for way too many people i know. Not only do not enough people understand the concept… not enough follow through and zero properly. Heaven forbid something would take time, effort, and a bit of expense.
Good explanation Ed and thanks to CTD for publishing another useful article that everyone and their dog should read.
The M1 Garand, has probably the most accurate open sights of any firearm, maybe because it has an almost 4 foot sight radius, and a Ballistic Compensating Sight. LOL
The manual says to ZERO it a 200 yards, and when that is accomplished, then the rear Ballistic Compensating Sight (Thats interesting), can be dialed up to 1,200 yards. While I could probably hit the bullseye at 1,200 yards with an M1, the bullseye may have to be the size of NYC. LOL
We started at 25 meters with the M16… worked out to 300…
In civilian life… I sorta cheat somewhat…
I bore sight using a laser and reflective target at 25 yards to center of target.
Then test fire on paper at what ever range I intend to use the that particular rifle for.
Usually very little fine tuning is needed.
Works for me and doesn’t burn a ton of ammo in the process.
that 50-200 rule can vary some with calibers but it is and has been true since I was young…I am 73 years young
@Ed, sent this three times, but didn’t show.
Great Topic, and nice article. “An AR-type rifle that is typically zeroed at 100–200 yards can shoot well beyond 300 yards”. I think the AR 5.56 platform is kind of an exception, as do to the design, any iron, Red Dot, or Scope has to be mounted rather high, compare to more hunting style platforms. This actually turns out to be an advantage, as it can maximize on what is referred to as the 50/200 yard ZERO. What that means is: Let say, or rather use 2″ just to make it easy, that the centerline of the bore on an AR, to the sight, Red Dot, or Cross-hairs, is an even 2″. With this it is really worth while to get a really good Point Of Aim ZERO at 50 yards, because then at 100 yards it will Point Of Impact about 2″ high, BUT then at 200 yards it will Point Of Impact back to Zero again, and less than 50 yards it could Point Of Impact as much as 2″ low. In other words, the 50/200 method basically gives you a Point Of Aim ZERO, for Point Of Impact, from the tip of the barrel all the way out to 200 yards, +/- 2″.
Great Topic, and nice article. “An AR-type rifle that is typically zeroed at 100–200 yards can shoot well beyond 300 yards”. I think the AR 5.56 platform is kind of an exception, as do to the design, any iron, Red Dot, or Scope has to be mounted rather high, compare to more hunting style platforms. This actually turns out to be an advantage, as it can maximize on what is referred to as the 50/200 yard ZERO. What that means is: Let say, or rather use 2″ just to make it easy, that the centerline of the bore on an AR, to the sight, Red Dot, or Cross-hairs, is an even 2″. With this it is really worth while to get a really good Point Of Aim ZERO at 50 yards, because then at 100 yards it will Point Of Impact about 2″ high, BUT then at 200 yards it will Point Of Impact back to Zero again, and less than 50 yards it could Point Of Impact as much as 2″ low. In other words, the 50/200 method basically gives you a Point Of Aim ZERO, for Point Of Impact, from the tip of the barrel all the way out to 200 yards, +/- 2″.
Great Topic, and nice article. “An AR-type rifle that is typically zeroed at 100–200 yards can shoot well beyond 300 yards”. I think the AR 5.56 platform is kind of an exception, as do to the design, any iron, Red Dot, or Scope has to be mounted rather high, compare to more hunting style platforms. This actually turns out to be an advantage, as it can maximize on what is referred to as the 50/200 yard ZERO. What that means is: Let say, or rather use 2″ just to make it easy, that the centerline of the bore on an AR, to the sight, Red Dot, or Cross-hairs, is an even 2″. With this it is really worth while to get a really good Point Of Aim ZERO at 50 yards, because then at 100 yards it will Point Of Impact about 2″ high, BUT then at 200 yards it will Point Of Impact back to Zero again, and less than 50 yards it could Point Of Impact as much as 2″ low. In other words, the 50/200 method basically gives you a Point Of Aim ZERO, for Point Of Impact, from the tip of the barrel all the way out to 200 yards, +/- 2″.
Thanks again Ed. Just one more item to add to my to-do list.
@DR.HESS. If you have the ability to access a Magpul video, I believe it was titled The Art of the Precision Rifle or something like that, it may be of interest to you. It was a long distance instructor, teaching other instructors how to shoot up to a mile with like a .308. The instructor didn’t need or use any of the modern “dope” systems, he just did it all in his head, including cross wind effects. Impressive to say the least. Near the end of the video he covered what you commented on, but he said the trajectory arc is a myth, and set out to prove it. I think he put it like: One day out shooting I stumbled across the fact that the trajectory arc is a myth. He did so by putting up two bed sheets, I believe the first one was at 1,000 yards, and the second one 10 yards directly be hind the first. One of the students took a single shot, piercing both sheets. The class then went down and he told them to put a nail in the side board at the hight of each hole, in each sheet, basically representing the bullet drop in that 10 yards @ like 1,010. He then instructed them to tie a string from the first nail to the second nail. Then he told the student who took the shot, to sight up that string, and tell me what you see. The student sighted up the string and replied: “I see my rifle”. The instructor asked: Is that not a straight line? I am not able to prove or disprove this test, but it sure was an interesting video. In the beginning of the video, he had all the students zero their scopes, then take them off, and pass it to the student to the right of you. They then proceeded to start class at I believe 650 yards, and most got it on the first shot, using a scope sighted in on another rifle. I wish I had that video so I could see it again. It did get me interested in precision rifles. 🙂
Minor note: Bullet trajectory is not a parabola. It is not symmetrical. There’s lots of maffs involved (calculus.) At every single point along the path, the bullet is going slower than it was at the point before it, unless you’re shooting in a vacuum. So, the bullet is dropping much more per unit of distance at 100 yards than it is at 10 yards, for example. At 100 yards, it might drop 3″ from line of sight (first 100 yards,) but at 500 yards, it may drop 5″ or even 10″ in just the last 100 yards.