Spoiler:
What distance should you zero the sights or optic on your AR-15 style rifle? For the flattest, set-it-and-forget-it trajectory, zero your red dot, holographic, and backup sights at 50 yards. Trust us, or keep reading to find out why.
When adding a red-dot optic and backup sights you will want to:
Choose the best optic and backup sights for your needs.- Decide if you want your backup sights cowitnessed or in the lower 1/3 of the optic’s window.
- Install your electronic optic onto your rifle and add backup sights just in case your electronic optic fails. (Don’t forget to use Loctite thread locker on all the screws.)
- Choose the best “battle zero” (BZ) for your rifle, and then zero it at the range.
- Co-witness the backup sights with the reticle of the electronic sight, or if you chose a lower 1/3 witness, then zero your backup sights independently.
- Carry spare batteries with the rifle, such as in the grip or in your support gear.
Red Dot Sights (RDS) and Holographic Weapons Sights (HWS):
Shooting from CQB distances out to 200 meters and beyond can greatly be aided with the use of red-dot or holographic electronic optics. They are much easier to shoot with than traditional iron sights.
Buy quality gear. Cheap sights may not be bright enough to be seen on bright, sunny days. Also, they may not be handle the rough and tumble abuse from run’n and gun’n… mounts may break off, electronics may fail, or glass may easily crack.
As with all firearm accessories, make sure to use Loctite on all screw threads. You optic’s mounts will eventually vibrate loose. You will have to remount and rezero your optic.
Backup “Iron” Sights (BUIS):
If you are going to use backup sights as a redundancy for your red-dot sight (RDS) or holographic sight, zero the optic first (reason discussed below). Then pop up your backup sights and match them to optic’s reticle so that the front sight post bisects the red-dot aiming reticle while looking through the sights.
If you are going to use backup sights as a stand alone aiming system, zero them at 50 yards. Zero as accurately as possible, but do not get frustrated if they are slightly off.
This page does not pertain to A2 style AR-15 sights that are adjustable for different ranges.
Be sure to use Loctite thread locker on the sight’s screws when mounting them to your rifle.
What Distance To Zero Your RDS and BUIS:
Battle Zero
- 50/220 Yard Zero
- USMC 36/300 Yard Zero
- USMC 200 Yard Zero
If you don’t have the patience for a detailed explanation, then you will still be well served by the information above. If you want to know more, keep reading.
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Disclaimer:
I used the iPad application “Ballistic” (pictured right) to generate the data to create ballistic trajectory graphs for M855 62-grain and M193 55-grain FMJ ammunition with AR15 sights sitting 2.5″ above the center of bore.
I used “standard weather” (15º C / 59ºF, pressure 29.92, sea level altitude), and zero wind direction/velocity.
For ballistic calculations I used the following velocities:
- 20″ barrel / M855 62-grain FMJ — 3061 FPS
- 20″ barrel / M193 55-grain FMJ — 3254 FPS
- 16″ barrel / M855 62-grain FMJ — 2938 FPS
- 16″ barrel / M193 55-grain FMJ — 3075 FPS
- 14.5″ barrel / M855 62-grain FMJ — 2861 FPS
If you use a different type of ammunition (manufacturer, weight, bullet type), barrel length, sight height over bore, or shoot at a different altitude with a different temperature, barometric pressure, and with wind you can expect deviations from the ballistic solutions that I have provided.
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Flat-Top AR15 Rifles With Removable Carry Handles:
Most AR15 style rifles built in the past ten to fifteen years do not have a built in carry handle / rear sight assembly, but rather a “Picatinny rail” that allows the user to have a choice as to mount holographic sights, red-dot sights, magnified optics, simple rear sights, or even a removable carry handle / rear sight assembly. These are referred to as “flat top” rifles. In the past, anyone wanting to mount optics on top of their AR-15 style rifles were forced to use some type of adaptor to mount their optics on top of the fixed carry handle. This set the optics too high to take advantage of the 5.56x45mm NATO rounds fairly flat trajectory, and it set the optic too high for the shooter to get a good cheek weld on the stock. The flat-top design allows you to mount your optics so that the aiming reticle is the same height above bore as the tradition fixed “iron sights”.
Some flat top rifles are sold with a removable carry handle that looks exactly like the older fixed carry handles, except that they can be easily removed with two knobs. Some rifles are sold without the carry handle as manufactures realize that most end users will want to remove them to customize their rifles with optics and accessories. If you choose to simply use the carry handle then don’t mount any optics to the top of it. This defeats the purpose of the removable carry handle. Remove it and mount the optics to the rifle’s rail.
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Red-Dot Sights (RDS) and Holographic Weapons Sights (HWS):
Red-dot optics reduce the number of points in a proper sight picture from three to two. Instead of aligning the target with the front sight post and a rear notch, it is only necessary to place the dot on the target. At night, when used with a weapons light, it is highly visible against the dark background.
More details on the subject of red-dot and holographic sights can be found on the linked page above, but without being repetitive with the other page I would highly recommend the Aimpoint “PRO” (Patrol Rifle Optic) red-dot sight (pictured right), or the Eotech’s 512 holographic sight. Both are high quality optics that are purpose built for AR15 style rifles and are the correct height to co-witness with backup sights (discussed further in the article).
Other Quality RDS Optics That Are Correct Height For AR-15 Rifles And Don’t Require Any Spacers Or Risers:
- xxxxxxxxxxxx
Always keep spare batteries for the optic with the rifle. I really like Magpul’s MOE grips (pictured right) as they have a compartment where you can store spare batteries for your optic or weapons light. I place the battery in a small plastic arts & crafts “crack bag” before storing it in the grip. (If you replace your grips, be very careful as there is a very small spring and pin that may fall out when you remove the original grip. Be careful not to damage the spring when installing the new grip. Be sure to add a dot of Loctite to the screw that holds the grip to the rifle’s receiver.)
Be sure to add a Backup Iron Sight (discussed next) as batteries can go dead and electronics can fail or be destroyed. With backup sights you will be able to stay in the fight.
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Backup Sights To Complement Red-Dot or Holographic Sights:
BUIS is an acronym for “backup iron sights”. This is nothing more than a catchy label for backup sights that you can use when and if your primary electronic or magnified optic is damaged or fails. “Iron” simply refers to their metal parts to differentiate them from electronic optics, although none of them are made from iron, but rather aluminum, steel, and plastic. Backup sights can simply be a rear sight that sits on a flat-top receiver behind the optic, or it may be a set of both front and rear sights for an ORC (Optic Ready Carbine: a carbine with only rails on top and no front sight base that is ready for customization by the end user).
If you run some type of aiming device (holographic sight, red-dot sight, or magnified optic) on your rifle then you need to have a backup sight(s) on your rifle. Murphy’s Law dictates that your electronic optics will break or be damage, your scopes will break or fog up, and your batteries will go dead at the worst time. If this happens and you don’t have a backup system for aiming, then that weapon is out of the fight. You soon will be too.
One day, after making a long drive to the range to shoot my M4, I discovered that my Eotech’s batteries were dead. Although I was ashamed for not having an extra set of batteries with my rifle or in my range bag, I was still able to utilize the rifle’s backup sights and enjoy a long morning of shooting. Fast forward to the present: Besides installing backup sights on all of my rifles, I store an extra set of batteries in each rifle’s Magpul MOE aftermarket pistol grips, and keep extra batteries in my range bag.
Stay away from cheap Chinese made “Airsoft” quality parts and gear, such as Aim Sports, Promag, Leepers, UTG or NcStar. Save your money and buy quality gear. Your life may depend on it. As always, when you install any parts, be sure to use Loctite thread locker on the threads of the screws to keep your parts from loosening up when you shoot.
Manufactures of Quality Backup Sights include:
If you are going to install backup sights on a Bushmaster brand carbine, be sure to read:
Zeroing Backup “Iron” Sights:
If you are going to use BUIS to backup your optic as they are intended, then keep them folded down and out of the way until the optic fails or is damaged. Then simply pop them up into position and use them while looking through the dead optic. If the optic is too damaged to look through, then if you have equipped it with a quick release mount and can remove it out of the way so that you can continue the fight with the backup sights.
BUIS Zeroing Procedure:
Most backup type sights do not have as many fine, incremental adjustments as the RDS that they will backup. You won’t be able to adjust the backup sight as finely as you will the optic. The most efficient method is to finely zero your optic first, and then match your BUIS as close to the RDS as possible (don’t get upset if you can not get it to match perfectly). You will want to zero the RDS with the sights folded down and out of the way. Then you pop up your backup sights, and while looking through both the backup sights and the optic, adjust the sights so that the reticle (the red dot) of the RDS bisected across the middle by the top of the front sight post. With a properly zeroed RDS you can zero your BUIS without firing a shot. Simply match them to the RDS.
Unlike A2 sights, with most backup style sights you zero your elevation setting to your desired battle sights zero (BSZ) and leave it. Your elevation will be adjusted with the front sight, and windage will be adjusted with the rear sight.
BUIS Sight Adjustments:
When adjusting the sights on any firearm, remember the acronym, “FORS”. Front Opposite, Rear Same. For firearms that require you to move the front sight to adjust bullet impact, you will want to move your sight in the opposite direction that you want to move the shot group. If you have to adjust the rear sight, then you move it in the same direction that you want your bullet group to move.
Adjust Elevation On The Front BUIS:
Use the acronym, FORS. Front Opposite, Rear Same.
- To raise your next shot group, rotate the front sight post clockwise.
- To lower your next shot group, rotate the front sight post counterclockwise.
Adjust Windage On The Rear BUIS:
Again, use the acronym, FORS. Front Opposite, Rear Same.
- To move your next shot group to the left, turn the windage knob counterclockwise.
- To move your next shot group to the right, turn the windage knob clockwise.
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Ballistics Review:
- Bullet Trajectory: Fact and Myth
- Throwing Lead’s article Ballistics of Modern Firearms
- Throwing Lead’s article on Basic Ballistics
- Throwing Lead’s Short Course in External Ballistics
Ballistics Terms:
Battle Sight Zero (BSZ) or Battle Zero (BZ): The USMC defines BSZ as the elevation and windage settings required to place a single shot, or the center of a shot group, in the center of a target at 300 yards/meters, under ideal weather conditions (i.e., no wind). A BZO is the sight settings placed on your rifle for combat. In combat, your rifle’s BZ setting will enable engagement of point targets from 0–300 yards/meters in a no wind condition. 8/3 is the rear sight elevation setting for the M-16A2 BZO. 6/3 is the rear sight elevation knob setting for the M-16A4 and M4 Carbine.
Centerline of the Bore: An imaginary straight line beginning at the chamber-end of the barrel. It proceeds out of the muzzle and continues indefinitely.
First Zero: Unless a bullet is stopped first, it will pass through the line-of-sight or point-of-aim two times. The first point that it crosses line of sight is refereed to as the first zero. When you refer to a trajectory, such as “25/300 meter zero”, you are saying that the bullet passes through the point-of-aim at 25 meters and again at 300 meters. 25 meters would be the first zero.
Line-of-Sight: This is the same thing as Point-of-aim. It is the imaginary straight line that starts at your eyes, passes through the center of the rear sight aperture. Then, it continues across the tip of the front sight post to the exact point of aim on the target.
Point-of-Aim: The aiming point is the precise point where the tip of the front sight post is placed in relationship to the target. It is the point where you wish the bullet to strike.
Point-of-Impact: This is the place where the bullet hits the target. It is usually described as “+” and the number of inches of deviation if it is occurs above the point-of-aim, or “-” and the number of inches of deviation if it occurs below the point-of-aim. Example: “+1.3 at 200 meters” means that the bullet should impact 1.3 inches above your point-of-aim at 200 meters.
Point-of-Aim = Point-of-Impact (POA=POI): To accurately engage targets, the strike of the bullet must coincide with the aiming point (Point of aim/point of impact) on the target. This must be done while compensating for the effects of wind/weather and the range to the target. This is accomplished by adjusting the sights on your rifle to achieve point of aim/point of impact. This process is called zeroing and it is the basic and most critical element of accurate target engagement, along with sound/solid understanding of the marksmanship fundamentals. One can not work with out the other to place a shot or shot group in the center of the target at any given distance.
Second Zero: Unless a bullet is stopped first, it will pass through the line-of-sight or point-of-aim two times. The second point that it crosses the line of sight is refereed to as the second zero. When you refer to a trajectory, such as “25/300 meter zero”, you are saying that the bullet first passes through the point-of-aim at 25 meters and again at 300 meters. 300 meters would be the second zero.
Trajectory: A bullet does not follow a straight line to the target. Instead, a bullet travels in a curved path, or arc, which is called the bullet trajectory.
Zero: A zero is the elevation and windage settings required to place a single shot, or the center of a shot group, in center of the target at a specific range, from a specific firing position, under specific weather conditions.
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What Distance to Zero Non-Magnified Optics & Sights:
Battle Sight Zero = Set It And-Forget It:
Simply zero your rifle for point of sight / point of impact at 50 yards. Make adjustments until bullet impact is right on the red dot. For shots at 300 meters simply hold over approximately one dot.
As discussed earlier, if you are going to install any type of electronic aiming device, it would be prudent to install some type of backup sights. You will also want the backup sights to be zeroed at 50 yards. With the optic and the backup sights properly installed and zeroed, it will look like the aiming dot of the optic is bisected by the top of the front sight post. The sights and optic will then be considered “co-witnessed”.
Simply defined, “Battle Sight Zero” (sometimes referred to as “Battle Zero”, “BSZ”, or “BZ”) is a theoretical “set it and forget it” setting for your backup sights or non-magnified optics that will allow your to make combat effective hits out to a certain distance without applying any hold-over or hold-under from your point-of-aim. With your sights set to a “Battle Sight Zero” you will know that your rounds will hit no more than “X” inches above or below your point-of-aim from CQB distances out to “Y” yards or meters distance. You will want your sights set at a distance that will provide the flattest trajectory, and thus the least deviation in point-of-aim and point-of-impact at varying distances. Fortunately for those using .223 Remington / 5.56mm NATO rifles, there is a distance that you can zero your rifle and enjoy a very flat trajectory out past 200 yards away.
What Zero Distance Provides The Flattest Trajectory?
It is important to zero the elevation of the sights with a single setting that will take the most advantage of the flat shooting trajectory of the 5.56mm/.223 caliber rifle round. The following diagram compares the trajectories of bullets when zeroed at 25, 50, and 100 yards. While you can expect minor variations in trajectory depending on if you are using a carbine with a 16″ barrel or a full-size battle rifle with a 20″ barrel, as we as with different brands, loads, and weights of ammunition, the data supplied is accurate enough to compare trajectories for use with backup sights and non-magnified optics.
100 Yard Trajectory:
The first chart shows the trajectory of a 5.56mm NATO round when fired from an AR15 style rifle. The dash line represents the shooters point of aim. The bullet departs the barrel approximately 2.5″ below the point of aim. It’s flight path reaches the shooters aiming point at 100 yards (point-of-aim (POA) = point-of-impact (POI). The bullet then drops back down to 2.5″ below POA at 200 yards, and plummets drastically after that. This isn’t a terrible zero if you never plan on shooting past 200 yards as the bullet will impact somewhere within the distance of the barrel to the top of the rifle’s sight base. Not terrible, but you can do better.
If you want to use a 100 yard zero trajectory, use these near zero distances to initially zero your rifle:
- 20″ Barrel Rifle Near Zero: xx
- 16″ Barrel Rifle Near Zero: xx
25/300 Meter Trajectory:
The next graph represents the traditional US Army method of zeroing the M4 carbines at 25/300 meters (meaning that you zero the rifle at 25 meters and can expect a second POA = POI at 300 meters). This was traditionally done with adjustable rear sights, such as those found on rifle’s equipped with carry handles, set on the 300 meter setting, but the target set 25 meters away. This is a not a very effecient zero setting. At 100 meters (109 yards) the your rounds will impact over 4″ above your POA. At 175 meters the bullet impact will reach its peak apogy at roughly 6″ above your POA. The USMC has finally accepted that this isn’t the most efficient way to zero an AR15 / M16 style rifle. Do not use a 25 meter “set-it-and-forget-it” zero.
If you want to use a 25/300 meter zero trajectory, use these near zero distances to initially zero your rifle:
- 20″ Barrel Rifle Near Zero: xx
- 16″ Barrel Rifle Near Zero: xx
50/220 Yard Trajectory:
The next graph illustrates the ballistic trajectory of a 5.56mm NATO round with a 50 yard zero (not meters). This zero is commonly referred to as “Improved Battle Sight Zero”. As with the graphs above, you can see that the bullet leaves the rifle 2.5″ below the point-of-aim (POA). The bullets trajectory will pass through the shooters point-of-aim at 50 yards. At 100 yards it impact approximately 1.5″ high. It will reach its peak apogy of 1.8″ at approximately 140 yards. Around 220 yards the round will again pass through the shooters (POA). At 250 yards the round will impact approximately 2.5″ below POA. This data shows that on its flight from the rifle’s muzzle out to 250 yards, the bullet will hit somewhere within plus or minus the height of the rifles front sight base (+/- 2.5″). That’s pretty darn flat.
If you want to use a 50/220 yard zero trajectory, use these near zero distances to initially zero your rifle:
- 20″ Barrel Rifle Near Zero: xx
- 16″ Barrel Rifle Near Zero: xx
50 Yard, 25 / 300 Meters / 100 Yards Trajectory Comparison:
The final graph compares all three trajectories. The 100 yard zero isn’t terrible, but you can do better. The 25 / 300 meter zero is terrible. The 50 yard zero will provide the combat shooter with the flattest trajectory out to approximately 250 yards, and is the recommended distance to zero your backup sights and non-magnified optics as a “set it and forget it” Battle Sight Zero setting.
Conclusion and Recommendations:
The 50 yard zero provides the flattest trajectory for the AR-15 style rifle. It is easy to see why the 50 yard zero is the best choice, and how your point-of-impact will never be more than +/- 2.5 inches from your point-of-aim, from close up and personal “bad breath” distance, all the way out to a distance of approximately 250 yards. Competitive shooters and the USMC now realize this and employ the 50 yard zero technique with backup sights and non-magnified red-dot and holographic optics.
The final graph compares all three trajectories. The 100 yard zero isn’t terrible, but you can do better. The 25 / 300 meter zero is terrible. The 50 yard zero will provide the combat shooter with the flattest trajectory out to approximately 250 yards, and is the recommended distance to zero your iron sights and non-magnified optics as a “set it and forget it” Battle Sight Zero setting.
Important: This Battle Sight Zero is for AR-15 style rifles firing 5.56mm NATO ammunition. It is not necessarily an appropriate Battle Sight Zero for other 5.56mm rifles (because they may have sights of different height over bore than the AR-15), or rifles in other calibers. This is not the correct zero for Tavor, Steyr AUG, or AK rifles chambered in 5.56mm.
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Co-Witness Iron Sights and Optics:
What Is Co-Winess?
How To Co-Witness RDS and BUIS:
The easiest way to co-witness your optic and backup sights will be to carefully zero your optic first on the range so that your bullets are hitting exactly where you aim at 50 yards. You want to zero your optic first because it can be more finely adjusted than most backup sights. Next you will zero your backup sights. If your optic is correctly zeroed then you won’t have to fire a single shot to zero your backup sights. With the majority of backup sight you can not adjust the elevation of the rear sight. You must use a front sight post adjustment tool to raise or lower the front sight until it appears, when you are looking through the front and rear backup sight, that the optic’s reticle is horizontally bisected by the tip of the front sight post.
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The Savannah Arsenal Project 