The Savannah Arsenal Project

Spoiler:

This Is A Lot Of Information To Digest.  Skip To The Chase:

When I started researching this subject to satisfy my own curiosity I had no idea of how complex it would get, especially having to figure out zeros and trajectories for different barrel lengths and ammunition weights. As a reader it will be easy to get bogged down and overwhelmed by all of the minutia that I’ve bombarded you with.

You will be served by reading about the battle zero philosophy and the four different zeroing techniques here in the spoiler section, decide on which zeroing technique will best serve your needs, and then skip down to that technique’s detailed description. In that section, find the rifle barrel length and ammunition type that matches yours (ie. USMC method – 16″ barrel – M855 ammunition) and zero accordingly. You will probably want to save your time and energy by skipping the reading for the zeroing technique and rifle/ammunition combinations that don’t pertain to you.

A2 Sights, Their Parts, And How To Adjust Them Are Discussed:

There is very basic review of ballistics and a review of A2 sights and how to use and adjust them.  This is a good review, even if you think that you already know everything about them (I thought that I knew everything about A2 sights, but I learned a great deal while researching this).

The Battle Zero (BZ) Philosophy Is Discussed:

The term “Battle Zero” (or “Battle Sight Zero”) is a misleading term.  It isn’t an actual specific sight setting, but rather a philosophy of employing a zero distance that will keep the point-of-aim and the bullet’s actual path within a certain acceptable margin out to the longest possible range.  It will provide the flattest trajectory over the longest distance and allows you to aim at center mass of the target and achieve hits within +/- X inches out to a distance of Y meters or yards.  Intended as a method for combat shooting over varying distances, the soldier can simply aim at his rifle into the middle of an enemy at an unspecified distance and know that he will hit within a lethal zone without worrying about holding over or under the target.

Four Different Ways To Zero And Employ A2 Sights Are Discussed:

The US Army Method:

• Method of use originally conceived for 14.5″ M4 barrel carbines, but adaptation for other barrel lengths is addressed.
• Zeroed with the small aperture, at 25 meters, with the 6/3 setting, for a 25/300 meter zero.
• The sights are calibrated for the 300, 400, 500, and 600 meter settings with their respective distances.
• Use the 6/3 setting with the 25/300 meter trajectory as BZ.
• Flip from the small aperture to the large “0-200” aperture for a 200 meter zero.  Use the large aperture for “close range” and “low light” shooting.
• More details about this method, as well as procedures for adapting this method for 20″ barrel rifles and 16″ barrel carbines are described further down the page.

The USMC Method:

• Marines still use yardage with regards to marksmanship.
• Marines only use the small rear sight aperture.  Never the larger “0-200” aperture.
• Method of use originally conceived for 20″ barrel rifles, but adaptation for other barrel lengths is addressed.
• Rear sight is armorer modified so it can be dialed down two clicks below the 8/3 setting (“8/3-2”), or down four clicks below the “6/3” (“6/3-4”) setting on rifles with a removable carry handle.
• Zeroed with small aperture at 36 yards on the “8/3” or “6/3” sight setting for a 36/300 yard zero.
• For BSZ, Marines dial down two clicks below the “8/3” setting, or four clicks below the “6/3”, for a ≅ 55/200 yard trajectory.
• More details about this method, as well as procedures for adapting this method for 14.5″ and 16″ barrel carbines are described further down the page.

The Santos Improved Battle Zero (SIBZ) Method:

• Method of use originally conceived for 20″ barrel rifles, but adaptation for other barrel lengths is addressed.
• The rear sight is calibrated for the 300, 400, 500, and 600 meter settings with their respective distances, however it is modified so that there is a setting for a 50 yard/200 meter zero trajectory.
• Like USMC rifles, the rear sight is modified so that it can be dialed down two clicks below the “8/3” setting, or down four clicks below the “6/3” setting on rifles with removable carry handles.
• When sight is dialed down to the “8/3-2” or the “6/3-4” setting it is now zeroed for a ≅50 yard/200 meter trajectory.  This setting is used as the BSZ.
• More details about this method, as well as procedures for adapting this method for 14.5″ and 16″ barrel carbines are described further down the page.

The Revised Improvised Battle Zero  (RIBZ) Method:

• The rear sight is calibrated at for the 300, 400, 500, and 600 meter settings with their respective distances, however it is modified so that there is a setting for a 50 yard/200 meter zero, as well as an additional setting for 100 yard zero.
• The sight is modified so that it can be dialed down a total of three clicks below the “8/3” setting on a fixed carry handle rifle (“8/3-3”), or six click below the “6/3” setting on a removable carry handle rifle or carbine.
• As with the Santos method, when the rear sight is dialed down two clicks below the “8/2” (“8/2-2″) on a 20” rifle with a fixed carry handle, the sights are calibrated for a 50 yard/200 meter zero.  When the sight is dialed down an additional click (“8/3-3”), the sight is now calibrated for ≅100 yards.
• On a rifle or carbine with a removable carry handle the values are doubled.  When the sights are dialed down 4 clicks (“6/3-4”) the sights are calibrated for a ≅50 yard/200 meter zero.  When the sights are dialed down another two clicks (“6/3-6”) the sights are now calibrated for ≅100 yards.
• More details about this method are described further down the page.

This Page Does Not Address:

• Older Style A1 Sights.
• Backup “Iron” Sights.  Read more about setting up backup sights, as well as red dot sights (RDS) and holographic sights at Savannah Arsenal’s Adding Zero Magnification Electronic Sights and Backup Sights To Flat-Top AR-15 Rifles.

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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Contents:

• Disclaimer
• Ballistics Review
• AR-15 A2 Sights And The “Battle Zero” Philosophy
• A2 Sight Parts, Markings, and Settings
• Mechanical Process To Adjust And Zero The A2 Sights
• US Army Method — 25/300 Meter BZ
• United States Marine Corps Method — 200 Yard BZ
• Santos Improved BZ Method — 50 Yard/200 Meter BZ
• Revised Improved BZ Method — 50 Yard/200 Meter BZ, But Better
• Using A2 Sights With A CMMG .22LR Conversion Kit
• Factors That May Cause A Rifle To Need To Be Re-zeroed
• Related Pages

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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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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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AR-15 A2 Sights And The “Battle Zero” Philosophy:

Target Shooting vs. Combat Shooting:

With the sights properly zeroed, selecting a specific sight setting for a specific distance is great for bulls eye target shooting.  Example: Set the sight to the “2” setting when shooting at a target known to be 200 meters away.  Combat shooting is fairly more dynamic and the shooter will find themselves engaging targets at various (and unspecified) distances.  They don’t need to hit the absolute center of a bulls eye, but they need to be able to hit within a lethal zone on targets at various distances without having to adjust the sights or worry about holding over or under. They need to set up their sights so that they can hit somewhere within a small “box” at varying distances and not worry about shooting tight bulls eye groups.

Battle Zero (BZ):

The term “Battle Sight Zero” is a misleading term.  It isn’t an actual specific sight setting, but rather a philosophy of employing a zero distance that will keep the point-of-aim and the bullet’s actual path within a certain acceptable margin out to the longest possible range.  It will provide the flattest trajectory over the longest distance and allows you to aim at center mass of the target and achieve hits within +/- X inches out to a distance of Y meters or yards.  Intended as a method for combat shooting over varying distances, the soldier can simply aim at his rifle into the middle of an enemy at an unspecified distance and know that he will hit within a lethal zone without worrying about holding over or under the target.  Simply aim and shoot.  As the photo to the right demonstrates, using the BSZ, if you aim at the middle of any of these enemy soldiers, you will be able to achieve lethal hits somewhere in the red.  BSZ is specific to the weapon type, caliber, and the shooter’s preference.  Obviously for any given weapon and caliber, the further that the shooter is from the target, the bigger that the “target box” will be.

The process of zeroing red-dot sights (RDS) and backup “iron” sights (BUIS) is outside the scope of this article, however it is necessary to point out the importance of determining a good set-it-and-forget-it zero, because unlike A2 style sights, once they are zeroed they are not battlefield adjustable.  You need to find one Battle Sight Zero that will do it all.

A2 Sights And The Battle Zero:

All of the A2 sight zeroing methods discussed will initially involve zeroing the sights so that the bullet will impact point-of-aim at the respective distance & sight setting.  When the A2 rifle sights are properly zeroed, the bullets will impact at point-of-aim at 100 meters with the “1” setting, 200 meters with the “2”, 300 meters with the “3”, etc.  Where the methods differ are the BZ philosophies, and how they are achieved and employed.  The processes and results are discussed further below.

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A2 Sight Parts, Markings, and Settings:

The sighting system of the service rifle/carbine consists of a front sight post, a rear sight apertures with windage knob, and a rear sight elevation knob. Moving each of these sights one graduation or notch is referred to as moving one “click” on the sight system.

Front Sight:

The front sight consists of a square, rotating sight post with a four-position, spring-loaded detent.  The front sight is only adjusted during the initial zeroing procedure and then it isn’t ever manipulated again.  In the zeroing process discussed further down this page it states that the sight is initially set at the mechanical zero position (as seen in the photo to the right) where the flange at the base of the front sight post is flush with the top of the front sight tower.

Beginning with the rear sight on the correct setting for the zeroing process, the front sight is raised or lowered to move the shot group up or down until the rounds are impacting at the correct point.  At that point the sights are considered calibrated and any range changes are made with the rear sight drum.  More details discussed further down the page.

Front Sight Post Click Values — 20″ Barrel:

Each click of the front sight post moves the point-of-impact ≅ 1.25 MOA.  I’ve done the following math to speed you along.

• At 25 meters each click (1/4 turn) of the front sight post moves point-of-impact ≅ .9 cm / .35″.
• At 100 meters each click (1/4 turn) of the front sight post moves point-of-impact ≅ 3.5cm / 1.4″.

Front Sight Post Click Values — 16″ Barrel:

Each click of the front sight moves the point-of-impact ≅ 1.7 MOA.  I’ve done the following math to speed you along.

• At 25 meters each click (1/4 turn) of the front sight post moves point-of-impact ≅ 1.19 cm / .46″.
• At 100 meters each click (1/4 turn) of the front sight post moves point-of-impact ≅ 4.76cm / 1.84″.

Rear Sight — Normal Range Aperture:

The unlabeled aperture, pictured right, is used for distance shooting.  It is used in conjunction with the range elevation drum for 300, 400, 500, 600, 700, and 800 meter targets.

Normally your eye can only focus on one point in space. When shooting, your choices are to focus on the rear sight, or the front sight, or the target. When firing any other weapon you are always trained to focus on the front sight. The further the target, the more out of focus it will appear. The small aperture “tricks” your eye and allows you to focus on the front sight and yet still have an amazingly clear view of the far away target. The larger ghost ring sight can not do this.

Be sure to check out The New Rifleman’sUltimate Guide to the AR-15 Iron Sights Ver 1.1. The author is much smarter than the average Internet Commando and gives a detailed, yet easy to understand explanation of the genius of the small aperture rear sight and how it is designed to work with the shooter’s eye.

Rear Sight — Short Range “0-200” Aperture:

The larger “ghost ring” is a simple and quick aiming tool that is very useful in low light or close quarters shooting.  This larger “ghost ring” aperture is used for 0 – 200 meters range.  As seen pictured right, the sight is set for 0-200 meters.  It’s elevation aims 2.5 MOA (roughly 2.5″ at 100 yards) below the normal range aperture.  This larger aperture is only used when the rear sight is  down and aligned with the “6/3” or “8/3” indication on the rear sight’s range elevation selector.

Because of the larger diameter of the ghost ring’s hole, it is very important that the shooter center the front sight in their field of view when looking through the sight.  When shooting with the ghost ring you will want to focus on the target, and not on the front sight post as with all other types of firearm sights.  With this method the front sight will appear fuzzy, but at at close range this will be inconsequential.  This sight is intended for quick and dirty combat shooting, rather than precision shooting.

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Rear Sight — Range Elevation Drum:

When the rifle is properly zeroed, the range selector is used to select the distance in meters for which you want your bullet to impact.

There is a “8/3” setting on older rifles with a fixed carry handle, and a “6/3” setting on removable carry handles and stand-alone A2 sights.  When the range selector is set to its lowest position (or 2 clicks above its lowest position on US Marine Corps rifles) and is aligned with the “6/3” or “8/3” setting, the bullet should impact where you are aiming at 300 meters.  On the sights with a “6/3” setting there is a “4” (400 meters), and “5” (500 meters) setting.  With these settings you will hit where you aim at 400 and 500 meters respectively.  If you continue to rotate the range selector drum to the “6/3” setting again, you are now on the 600 meter setting.  Remember that when it is set for 600 meters then there will be a significant space between the carry handle and the rear sight base.  300 meters is the lowest setting and 600 meters is the higher setting of the drum.  For a fixed carry handle rifle there will be a “6” and a “7” setting.  You will continue to rotate and raise the range selector drum to the “8/3” for the 800 meter setting.  If you accidentally set your rifle to the 600 or 800 meter setting and shoot at a target 300 meters away, your bullets will impact approximately three and a half feet, or eight feet over your target, respectively.  It is very important to appropriately set your range to target.

As discussed earlier, the elevation adjustment settings on a fixed carry rifle will be marked with “8/3”, “4”, “5”, “6”, and “7”.  On these sights there will be four unmarked settings between each number that can be felt as a click when they are selected.  If you must set two positions past the 400 meter setting, then that particular setting is referred to as “four plus two”.  If you must set the sight down two setting below the 6/3 or 8/3 setting (technique used by the USMC, or with the Santose Improve Battle Setting, discussed further down), then that particular setting is referred to as “six three minus two” or “eight three minus two”.

“Z” Setting – Only For Removable Carry Handle Rifles With 20″ Barrels:

The “Z” setting (pictured right) is for used for zeroing 20″ barrel rifle with a removable carry handle when it is zeroed at 25 meters. This is because the near zero with the 20″ rifle is approximately 31 meters rather than 25 meters as with the 14″ or 16″ barrel “M4” version of the rifle.  The “Z” setting is used to compensate for using the wrong near zero.  Use the “Z” setting when zeroing a 20″ barrel AR-15 with removable carry handle at 25 meters.   The “Z” setting is never used with a fixed carry handle rifle, or a 14.5″ barrel or 16″ barrel carbines.

Range Elevation Selector Click Values — Fixed Carry Handle Sight — 20″ Barrel:

Each click represents ≅ 1 MOA (or 1.0″ at 100 yards).

• At 25 yards  each click will move your point-of-impact ≅ .25″.
• At 100 meters each click will move your point-of-impact ≅ 1″.
• At 200 meters each click will move your point-of-impact ≅ 2″.
• At 300 meters each click will move your point-of-impact ≅ 3″.
• At 400 meters each click will move your point-of-impact ≅ 4″.
• At 500 meters each click will move your point-of-impact ≅ 5″.
• At 600 meters each click will move your point-of-impact ≅ 6″.

Range Elevation Selector Click Values — Fixed Carry Handle Sight — 16″ Barrel:

Each click represents ≅ 1.5 MOA (or 1.5″ at 100 yards).

• At 25 meters each click will move your point-of-impact ≅ .375″ (3/8″).
• At 100 meters each click will move your point-of-impact ≅ 1.5″.
• At 200 meters each click will move your point-of-impact ≅ 3.0″.
• At 300 meters each click will move your point-of-impact ≅ 4.5″.
• At 400 meters each click will move your point-of-impact ≅ 6.0″.
• At 500 meters each click will move your point-of-impact ≅ 7.5″.
• At 600 meters each click will move your point-of-impact ≅ 9.0″.

Range Elevation Selector Click Values — Removable Carry Handle Sight — 20″ Barrel:

Each click represents ≅ .5 MOA (or 1/2″ at 100 yards).

• At 25 meters each click will move your point-of-impact ≅ .125″ (1/8″).
• At 100 meters each click will move your point-of-impact ≅ .5″.
• At 200 meters each click will move your point-of-impact ≅ 1.0″.
• At 300 meters each click will move your point-of-impact ≅ 1.5″.
• At 400 meters each click will move your point-of-impact ≅ 2.0″.
• At 500 meters each click will move your point-of-impact ≅ 2.5″.
• At 600 meters each click will move your point-of-impact ≅ 3.0″.

Range Elevation Selector Click Values — Removable Carry Handle Sight — 16″ Barrel:

Each click represents ≅ .75 MOA (or 3/4″ at 100 yards).

• At 25 meters each click will move your point-of-impact ≅ .187″.
• At 100 meters each click will move your point-of-impact ≅ .75″.
• At 200 meters each click will move your point-of-impact ≅ 1.5″.
• At 300 meters each click will move your point-of-impact ≅ 2.25″.
• At 400 meters each click will move your point-of-impact ≅ 3.0″.
• At 500 meters each click will move your point-of-impact ≅ 3.75″.
• At 600 meters each click will move your point-of-impact ≅ 4.5″.

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Mechanical Process To Adjust And Zero The A2 Sights:

This is the mechanical procedure for zeroing the A2 type sights on M-16 / AR-15 / M4 style rifles.  The process is thoroughly explained, except that the target distance that you should zero your rifle or carbine has been omitted.  I have been careful to exclude the specific distance to zero the rifle as there are several different zeroing philosophies that will be discussed further down.  This description is in this section to show you the mechanics of how to zero the rifle.  Continue reading and decide on which zeroing philosophy and technique will best fit your needs.  Then you can employ the appropriate distances and sight settings discussed with your adopted philosophy and zero your rifle accordingly.

 1: Adjust The Sights To The Mechanical Zero Position:

Mechanical zero is simply the mechanically centering of a weapon systems sights.

Adjust The Windage Mechanical Zero Position:

• This is a $10 way of saying that you need to start by centering the windage for the rear sight.
• For A2 “8/3” sights and A3 “6/3” sights flip the rear sight aperture so the small unmarked aperture is up.
• Center the rear sight by turning the rear windage knob until you align the windage notch on the down aperture with the center notch on the rear sight base, as seen in the photo to the right.

 Adjust The Rear Sight To The Elevation Mechanical Zero Position:

• This is a $10 way of saying that you need to set the elevation indication to a “neutral position”.
• “ARMY” rifles will have the 300 meter mark set on the last whole click before it bottoms out.  The mechanical zero setting is the “8/3” or “6/3” position, which is the lowest setting.
• “Marine Corps” rifles will have sights that can be lowered two more clicks below the 300 meter setting.  The mechanical zero setting is still the “8/3” or “6/3” setting, or two clicks up from the bottom.

 Adjust The Front Sight Post To The Mechanical Zero Position:

• To set the front sight post to initial sight setting, depress the front sight detent and rotate the front sight post until the base of the front sight post is flush with the front sight housing.
• The front sight post is moved up or down when zeroing the rear sight. Once the rear sight is zeroed, the front sight post should not be moved.

2: Fire and Adjust Your Shot Groups:

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.

• Set up a target at the distance appropriate to the zeroing philosophy that you have adopted.
• Verify that the small, unmarked aperture on the rear sight is selected.
• When zeroing at 25 meters, such as with the Army method described further down the page, verify that the elevation knob is set to “8/3+1″ for a fixed carry handle rifle with a 20” barrel, set to the “Z” setting for a removable carry handle rifle with a 20″ barrel (as seen in the photo to the right), and bottomed out on the 6/3 setting for a removable carry handle carbine with a 14.5″ or 16″ barrel.  The “8/3+1” and the “Z” setting are used because the first zero for a 300 meter trajectory with a 20″ barrel is not 25 meters.  The sights are “tricked” so that you can get the same results as if zeroing at their real first zero.  With the 14.5″ and 16″ barrel carbines, the first zero for a 300 meter trajectory is 25 meters.  The carbine is simply zeroed with the “6/3” setting — no tricks required.
• Using 62 grain M855 FMJ ammunition, fire groups of three carefully aimed shots from a beanbag or bipod rested position and check the target after each group.
• Adjust the sights as necessary so that point-of-aim = point-of-impact.
• Reference the section above to determine how many clicks that you need to move your shot group to the center of the bulls eye.

Elevation Adjustment:

• Use the acronym, FORS. Front Opposite, Rear Same.
• To raise your next shot group, lower your front sight post by rotating the front sight post clockwise.
• To lower your next shot group, raise your front sight power by rotating the front sight post counterclockwise.
• You can use the tip of rifle bullet to push in the pin that allows you to rotate and raise or lower the front sight post, but a front sight tool, such as pictured right, is inexpensive and will make the job painless and easy.

Windage Adjustment:

• Again, use the acronym, FORS. Front Opposite, Rear Same.
• To move your next shot group to the left, move the rear sight to the left by turning the windage knob counterclockwise.
• To move your next shot group to the right, move your rear sight to the right by turning the windage knob clockwise.

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US Army Method — 25/300 Meter BZ:

Savannah Arsenal Note:  When I started my research for this project I was admittedly pre-biased against the Army method and their BSZ philosophy.  After lots of research, ballistics calculations, and range time, I have decided that while it isn’t the most efficient trajectory, it isn’t as bad as I had thought.  I will go ahead and state that I think that there is greater utility in some of the other methods discussed further down the page, however this method is still very viable.  Whether or not I prefer this method, the fact remains that the US Army has put a lot of bad guys into the dirt using this method.

US Army Philosophy:

The US Army zeroes their 14.5″ barrel M4 carbines with 62-grain M855 ammunition at 25 meters with the “6/3” setting in order to achieve a 25/300 meter zero.  When you are zeroed at 25 meters with this configuration, your rear sight drum is calibrated as a bullet drop compensator for 300 meters using the small aperture.  Set the drum to “4” when shooting at 400 meters, “5” when shooting at 500 meters, and the higher 6/3 setting when shooting at 600 meters.

Flip from the small aperture to the large “0-200” aperture for “close range” and “low light” shooting.  Small aperture provide a ≅50 yard/200 meter zero.

25/300 Meter Battle Zero (BZ):

• For general shooting out to 300 meters, the US Army uses the “8/3” or “6/3” setting for their set-it-and-forget-it 25/300 meter “Battle Zero” (BZ).
• With a 25/300 meter zero from a 14.5″ or 16″ barrel carbine you can expect hits within +/- 7″ from the muzzle out to ≅350 meters (383 yards).
• With a 300 meter zero from a 20″ barrel rifle you can expect hits within +/- 6″ from the muzzle out to ≅ 350 meters.  Mathematically tighter than with the carbine, but not enough that you will notice when shooting.  Assume the same +/- 7″ performance with either length.

200 Meter Close Range / Low Light Battle Zero (BZ):

For distances from 0 to 200 meters, or for low light situations, the Army teaches to set the elevation drum to the lower 6/3 setting and use the flip to the large aperture.  This setting will provide you with a 200 meter (219 yard) zero.

• With a military’s 14.5″ barrel carbines, the near zero is approximately 42 meters (46 yards).
• With a 16″ barrel carbine the near zero is approximately 44 meters (48 yards).
• With a 20″ barrel rifle the near zero is approximately 47 meters (51 yards).
• These trajectories are too close for the shooter to concern themselves with.  For practicality, simply assume a 50 yard near zero.

Caveats For Army Technique With Other Barrel Lengths & Ammo Types:

The US Army uses the 25 meter (27.3 yards) / 300 meter (328 yards) zero.  This trajectory can be verified with ballistic charts with M855, 62-grain ammunition with a muzzle velocity of approximately 2860 FPS as when fired from a 14.5″ M4 barrel.

It is important to notice that the 25/300 meter zero is only valid with that exact ammunition — barrel length combination.  If you use the same ammunition in a rifle with a civilian 16″ or 20″ barrel, or if you use M193, 55-grain ammunition in any of those barrel lengths, you will have different near zeroes to achieve the same far 300 meter zero.  This also means that if you zero any of the other barrel lengths / ammunition combinations at 25 meters, then you will not achieve the 300 meter far zero.  Example: If you zero a full length (20″ barrel) AR-15 with 55-grain, M193 ammunition at 25 meters, then your trajectory will have your rounds impact a little over 5″ above your point-of-aim at 300 meters (328 yards).  Some shooters will not care about this fine detail, however the more skilled, detail-oriented shooters will.  These corrections are added here.

The “8/3+1” and the “Z” setting are used in the following procedures with 20″ barrel rifles because the first zero for a 300 meter trajectory with a 20″ barrel is not 25 meters.  The sights are “tricked” so that you can get the same results as if zeroing at their real first zero.  With the 14.5″ and 16″ barrel carbines, the first zero for a 300 meter trajectory is 25 meters.  The carbine is simply zeroed with the “6/3” setting (unless you change ammo) — no tricks required.

To achieve a 300 meter zero, rifles and carbines are zeroed as described earlier, but with the following caveats:

For Rifles With A Fixed Carry Handle A2 “8/3” Sight, and 20″ Barrel:

• Lower the rear sight all the way down by rotating the rear elevation drum counterclockwise. Then rotate the rear elevation drum clockwise UP one click above the “8/3” mark.
• With M855, 62-grain ammo: zero at 30 meters (33 yards).
• With M193, 55-grain ammo: zero at 31 meters (34 yards).

For Rifles With A Removable Carry Handle “6/3” Sight, and 20” Barrel:

• The A3 rear sight differs from the A2 in that its elevation index is marked “6/3” instead of “8/3”. Otherwise, the windage drum and flip-up aperture and their operation are the same as on the A2 rear sight.
• With M855, 62-grain ammo: zero at 30 meters (33 yards).
• With M193, 55-grain ammo: zero at 31 meters (34 yards).

-or-

• Using M855, 62-grain ammo, select the elevation dial TWO clicks clockwise UP past the “6/3” mark on the drum to the “Z” setting (see photo to the right).  Zero at 25 meters.

For Carbine With A Removable Carry Handle “6/3” Sight, and 14.5 or 16” Barrel:

• Same procedure as for A3 6/3 sights, except set the elevation drum on the “6/3″ setting, not the Z setting.
• With M855, 62-grain ammo: zero at 25 meters (27.3 yards).
• With M193, 55-grain ammo: zero at 27 meters (29.5 yards).

Deficiencies With The US Army’s 300-Meter Battle Sight Zero Method:

The US Army teaches that unless you are shooting at distances greater than 300 meters you should keep your rifle on the “6/3” or “8/3” setting and use the 300 meter BSZ trajectory setting as the your set-it-and-forget-it setting for all engagements out to 300 meters.  They also suggest that you should only flip the rear sight aperture to the “0-200” setting for low-light engagements.  This is flawed for a couple of reasons:

The 25 /300 Meter Zero Trajectory Is Not The Most Efficient “Battle Zero”:

The 25 / 300 meter trajectory is a very high arc, impacting 1.6″ above POI at 50 meters, 4.6″ above POI at 100 meters, 6″ above POA at 150 meters, 6.2″ above POA at 175 meters, 5.9″ above POA at 200 meters, and 3.9″ above POA at 250 meters.  This is a terribly inefficient trajectory, especially for targets closer than 250 meters, as stated earlier.

The Larger “0-200” Aperture Requires More Precision To Shoot Effectively:

The larger “0-200″ setting sits lower than the unmarked, smaller aperture and provides a trajectory with a 50 yard/200 meter (220 yards) zero.  This trajectory is very flat will provide the shooter a bullet trajectory +/- 2” from the muzzle out to just past 229 meters (250 yards).  This is a much better “battle zero” than the 25/300 meter zero.  I can only assume that the Army does not teach this method because they assume that it will be harder for the shooter to make as accurate shots with the larger “0-200” setting as with the smaller, non-marked aperture.  Personally I think that using the flatter trajectory from the larger “0-200” setting for any shooting under 229 meters (250 yards) would be more advantageous, however the US Army wants the soldier to reserve the “0-200” setting for low-light conditions.  Their logic is that it will be easier for you to see your target with the larger aperture with less light, but more precise shooting is possible with the smaller aperture during daylight.

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United States Marine Corps Method — 200 Yard BZ:

Marine Corps Method Philosophy:

Although the sights are calibrated in meters, the Marines still discuss yardage with regards to marksmanship.  Out of respect for those who have packed the gear to serve in the Corps I will not provide any yardage to meters conversions. Semper fidelis.

Marines only use the small rear sight aperture.  Never the larger “0-200” aperture.

Marines zero their 20″ barrel rifles for a 36 / 300 yard (not meter) zero with the “3” setting.   While as the rear sight on an Army M-16 or M4 (or civilian legal equivalent) will bottom out and not go down any further than the “8/3” or “6/3” setting, before a M-16A2 or M-16A4 rifle is ever issued to a Marine the rear sight is armorer modified so that it can be dialed down another two clicks down on a rifle with a fixed carry handle, or dialed down another four clicks down on a rifle with a removable carry handle.

When zeroed at 300 yards with the “8/3” or “6/3″ setting, if the sight is dialed down two clicks (with the fixed carry handle model) or four clicks (with the removable carry handle model), the sights are now zeroed for a ≅ 56 / 200 yard zero trajectory with a 20” rifle.  The trajectory of the 300 yard zero is very similar to the Army’s 300 meter zero, however the 200 yard zero is a very flat shooting trajectory, and much more efficient than the 300 yard or meter zero at distances typically employed with this type of rifle and caliber.  I have had several retired Marines tell me that they use to sight their fixed carry hand M-16 A2 rifles at 300 yards, but the dialed the sights down two clicks and used the 200 yard setting for most of their shooting.

Most Army and Marine veterans aren’t aware that the different branches of service set up their sights differently on the same type of rifle.

 36 / 300 Yard Zero (not meters) Trajectory:

Marines zero their 20″ barrel M-16 A2 and A4 so that with the “8/3” or “6/3″ setting the bullet impacts point-of-aim at 300 yards, not meters.  Where the US Army zeroes their rifles to achieve a 300 meter zero, the Marines must use a different near zero in order to achieve a 300 yards zero.  Using a rifle with a 20” barrel, M855 62 grain ammunition, and assuming a muzzle velocity of 3100 FPS, the near zero is 36 yards (not meters).  With a 36 / 300 yard zero on the 20″ barrel rifle you can expect:

• As already stated, a near zero of 36 yards.
• At 100 yards the bullet will impact ≅ 3.1″ above point-of-aim.
• At 150 yards the bullet will impact ≅ 4.35″ above point-of-aim.
• The bullet will reach the top of its trajectory ≅ 4.5″ above point-of-aim at 170 yards, and plateau at this height for another 10 yards.
• At 200 yards the bullet will impact ≅ 4.33″ above point-of-aim.
• At 250 yards the bullet will impact ≅ 3″ above point-of-aim.
• At 275 yards the bullet will impact ≅ 1.7″ above point-of-aim.
• The bullet will descend through point-of-aim again at 300 yards (as the name of the zero suggests), and then pass through 2.5 inches below point-of-aim at ≅ 330 yards (a little over 300 meters).

56 / 200 Yard Zero (not meters) Trajectory:

As discussed earlier, the Army’s method allows you to bottom out your sight to the “8/3” or “6/3” setting and flip the rear sight to the larger aperture with the “0-200” marking, and with that setting the rifle will be zeroed for an approximate 50 yard/200 meters trajectory.  The 200 meter zero with the “0-200” setting is a very flat trajectory, but as also discussed earlier, with the larger rear sight hole, achieving proper sight picture is challenging and the shooter must center up your front sight post within the rear sight hole much more precisely to achieve the same level of accuracy as with the smaller aperture.  As stated earlier, the Marines don’t use the larger sight aperture.  The Marine Corps method of adjusting the rear sight down two clicks below the 8/3 setting or four clicks below the “6/3” setting allows the Marine to shoot with a 200 yard zero (very similar to a 50 yard/200 meter zero), but with the accuracy potential of the smaller aperture.  WIN!  With the 200 yard zero the Marine can expect:

• A near zero of approximately 56 yards.
• At 100 yards the bullet will impact ≅ 1″ above point-of-aim.
• The bullet will reach the top of its trajectory at ≅ 1.2″ above point-of-aim at 127 yards, and plateau at this height for another 10 yards.
• The bullet will descend through point-of-aim again at ≅ 200 yards (as the name of the zero suggests), and then pass through 2.5 inches below point-of-aim at ≅ 250 yards.
• The Marine uses the precision of the small aperture to make hits within +/- the height of the front sight (2.5″) from the muzzle out to 250 yards without any adjustments.

Caveats For USMC Technique With Other Barrel Lengths & Ammo Types:

The Marine Corps method works perfectly with M855, 62 grain ammunition fired from an A2 configuration (20″ barrel, fixed carry handle), or A4 configuration (20″ barrel, removable carry handle).  If you use a carbine (shorter barrel = less velocity), or if you use a different weight ammunition (M193, 55 grain ammunition), then the perfect combination will be lost.

Below are the near zeros needed to configure your rifle or carbine at 300 yards with the “3” setting.  The rifle or carbine are zeroed as described earlier, but with the following caveats:

For Rifles With A Fixed Carry Handle A2 “8/3” Sight, and 20″ Barrel:

• Lower the rear sight all the way down by rotating the rear elevation drum counterclockwise. Then rotate the rear elevation drum up to the lower “8/3” mark.
• With M855, 62-grain ammo: zero at 36 yards.  Verify zero at 300 yards
• With M193, 55-grain ammo: zero at 37 yards.  Verify zero at 300 yards
• The trajectory with the 55 grain M193 and the 62-grain M855 ammunition is identical to within a few 100ths of an inch with the 300 yard zero. 
• Count on near identical performance with the sight selected to the “8/3 -2” or the “6/3 -4” setting.

For Rifles With A Removable Carry Handle “6/3” Sight, and 20” Barrel:

• The A3 rear sight differs from the A2 in that its elevation index is marked “6/3” instead of “8/3”.   Lower the rear sight all the way down by rotating the rear elevation drum counterclockwise. Then rotate the rear elevation drum up to the lower “6/3” mark.
• Otherwise, the windage drum and flip-up aperture and their operation are the same as on the A2 rear sight.
• With M855, 62-grain ammo: zero at 36 yards.  Verify zero at 300 yards
• With M193, 55-grain ammo: zero at 37 yards.  Verify zero at 300 yards.

For Carbine With A Removable Carry Handle “6/3” Sight, and 14.5 or 16” Barrel:

• Same procedure as for 20″ barrel rifle with removable 6/3 sights, except that the zero distances are different.
• With M855, 62-grain ammo: zero at 33 yards.  Near identical trajectory with the 20″ barrel, with biggest deviation of ≅ .6″ at 200 yards.
• With M193, 55-grain ammo: zero at 30 yards).  Near identical trajectory, with biggest deviation of ≅ .75″ at 200 yards. 
• Count on near identical 200 yard zero performance with the sight switched to “6/3 -4”.

Benefits Of  The United States Marine Corps Method:

With the rifle configured the US Marine Corps way and the rear sight set to “3”, the Marine can engage targets out to 350 yards and expect hits within +/- 5 inches of their aiming point.

By lowering the sight two clicks below the “8/3” or “6/3″ setting, the Marine can engage targets out to 250 yards and expect hits within +/- 2.5” of their aiming point, using the same precision small aperture as the 300 yard zero.

Marines, please comment at the bottom of the page if you see any discrepancies with this description.

Deficiencies Of The United States Marine Corps Method:

With regards to marksmanship, the United States Marine Corps still references yards instead of meters.  I find this peculiar since the sights on the rifle are calibrated for meters.  Some people will claim that meters and yards are so similar that it doesn’t matter.  While the yard-meter comparison may be splitting hairs at close distances, when you are shooting at distances in excess of 300 yards the differential really start to spread.  300 meters is 328 yards.  400 meters is a little over 437 yards, and 500 meters is almost 547 yards — almost half of a football field difference.  It matters.

The USMC method is the only one discussed on this page that doesn’t properly calibrate the sights for the appropriate distance with each setting.  When the rifle is zeroed so that point-of-aim = point-of-impact at 300 yards with the “3” setting, none of the other settings will be calibrated.  With the “4” bullets will not impact at your point-0f-aim at 400 meters or yards.  The same problem will happen with the “5”, “6”, “7”, and “8”, but the farther away, the more the problem will get exasperated.

If you are sure that none of your shooting will occur past 350 yards then the Marine Corps method is good to go.

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Santos Improved BZ Method — 50 Yard/200 Meter BZ:

An Improved Battlesight Zero for the M4 Carbine and M16A2 Rifle

by Lieutenant Colonel Chuck Santose, US Army (ret.)

Current Army/Marine Corps battle sight zero and it’s procedures are well described in TM9-1005-319-10, the M16/M4 operator’s manual.

The current 300 meter battle sight zero is a function of the sights on the rifle and I personally find it shoots too high for the vast majority of combat targets, including the Army’s qualification ranges. The procedure listed here takes better advantage of the flat trajectory of these rifles as well as the use of civilian ranges, which are seldom surveyed in meters.

When zeroed at 200 meters, a distance twice that of normal combat engagements, these rifles have a very flat trajectory that is less than 2″ from line of sight at all intermediate distances; a distance that’s smaller than the normal dispersion of arsenal or factory loaded ammunition. This tiny trajectory arc allows very precise shooting out to 250 meters where the bullet is only 2″ below line of sight.

A 200 meter zero has the happy coincidence of an initial trajectory cross-over at 50 yards, a distance available on almost all civilian ranges including many indoor ranges. This makes it easy to achieve a 200 meter battle sight zero without recourse to surveying your own range. If 200 meters is available you can fine-tune the zero at the real distance. And should when you get the chance.

The lowest sight setting, however, on these sights is 300 meters so the sight needs to be modified to preserve the markings on the sight (despite the fact that no one ever sets a range on these in the real world other than a USMC range). The sight needs to be set to bottom out at 8/3 -2 clicks. This will be the new 200-meter setting.

1. Flip the rear sight back to the unmarked aperture. This will reveal a hole in the top of the handle.
2. Rotate the sight wheel all the way down. Will probably be exactly at 8/3 (6/3). Don’t force it down.
3. Using a 1/16″ Allen wrench loosen the screw (under the revealed hole) in the sight wheel 3 full turns. Leave the wrench in the screw. (Note Chi-Com carry handles & sights use a 1mm Allen wrench)
4. Rotate the bottom half of the sight wheel two clicks clockwise. This will raise the sight body if you look at it while you’re turning it.
5. Tighten the Allen screw, remove the wrench, and confirm the sight bottoms out at 2 clicks BELOW 8/3.  If not repeat the procedure until it’s right.  Battle sight the rifle per the 10 with the following exceptions:  Sight should be at 8/3 -2 clicks, that is, all the way down, not up a click. Please note removable handle sights are marked 6/3 (rather than 8/3); also some are in ‘half-clicks’ as well. There should be 3 clicks between 3 and 4 on the knob. If there are 6 clicks then the sight needs to be set at –4 clicks (instead of –2).
6. Small aperture, nose to firing handle weld.
7. Distance is 50 yards.
8. Point of aim should be point of impact of bullet.
9. Remember you’re adjusting the FRONT SIGHT for elevation, not the rear, and that each click is about 1/2″ (actually a little more) at 50 yards. You won’t get it closer than that. Don’t frustrate yourself trying.

You’re done. Leave the sight in this position for 99% of your shooting.

If you have to shoot targets you KNOW are 300 meters away or more, just click to the right number on the sight.

If you’re patrolling set the sight to 8/3 and snap the aperture forward to 0-2. This will provide the same trajectory as above but with a larger, easier to see thru rear sight. Use this setting if you also have the M68 mounted as it’s quicker to transition to if the sight fails.

If you have an M68 CCO (Aimpoint CompM-XD) optical sight battle sight it to 50/200 as well. You can shoot to 300 meters by merely holding “over a dot.”

This battle sight zero is valid to 300 meters for both the M16A2 and M4 Carbines and their AR15 sisters. It’s valid with any ammunition that approaches the specs for M193 (55gr) or M855 (62g) Ball ammunition. It works for both rifles and carbines due to the offsetting influence of higher muzzle velocity in the rifle being offset by the longer sight radius that moves bullet strike less per click. This is battle sight, not X-ring shooting!

This battle sight zero does not reflect the doctrine of the US Armed Forces, however, it reflects the personal use of these weapons in combat and in training for over 34 years.

Santos Improved Battle Zero Philosophy:

Like the US Army method, the Santos Improved Battle Sight Zero Method provides proper calibration of the rifle’s sight settings for 300, 400, 500, 600 meters (and 700 and 800 meters with fixed carry handle sights). The Santos method, however modifies the rear sight so that there is a setting so that you can employ the very flat trajectory of a 50/≅220 yard (46/≅200 meter) zero.

The original Santos method was created for rifles with 20″ barrels and fixed carry handles.  Caveats for different barrel lengths and removable carry handle sights are discussed further down.

Just like with the Army’s method, the Santos Improved Battle Sight Zero method sets up your A2 sights so that you can use the lower “6/3” setting at 25 meters and 300 meters, the “4” at 400 meters, the “5” at 500 meters, and the higher 6/3 setting at 600 meters, however the Santos method adds the capability to use the very flat shooting 50 yard/200 meter zero.

As with the Marine Corps method, the rear sight is modified (technique discussed below) so that the sights can be adjusted down two clicks below the “8/3” setting or four clicks below the “6/3” setting.

Before you read any further let me warn you that the Santos Improved Battle Sight Zero will initially appear to very similar to the United States Marine Corps method.  Both involve modifying the rear sight so that sight settings can be selected two clicks below the “8/3” or four clicks below the “6/3” settings .  Where the modifications are the same, the zeroing technique is completely different.

The Marine Corps method involves zeroing the rifle for a 300 yard zero (not meters), and then adjusting the elevation knob two clicks below the “8/3” or four clicks below the “6/3” setting for a very flat shooting 200 yard (not meter) zero.  While the Santos Improved Battle Sight Zero procedure also involves modifying the rear sight, the rifle will still be 300 meter zeroed with the 8/3 or 6/3 setting, however when you adjust the elevation knob down two clicks below “8/3” or four clicks below “6/3”, the rifle will be zeroed for a 50 yard/200 meter zero.

Note that the near zero of a 200 meter zero is 50 yards (not meters).  This 50 yard/200 meter zero has a very flat trajectory out to 250 yards.  It is flat enough that I have been able to hit steel targets at 300 yards with the elevation knob still set for the 50 yard/200 meter trajectory. The 50 yard/200 meter zero is also recommended for red-dot optics and backup “iron” sights.

With the Santos technique, my sights were still able to hit steel targets at 400 yards with the “4” setting, and at 500 yards with the “5” setting.  The Santos Improved Battle Sight Zero gives the warrior the chance to employ a very useful, flat trajectory for battle scenarios within 300 meters, but still effectively use the other longer range settings on the sight.

Caveats For Santos Technique With Other Barrel Lengths & Ammo Types:

14.5″ Barrel Carbine:

As with the Army Method, zeroed at 25 meters for a 25/300 meter zero with the 6/3 setting.  For carbines with removable carry handles, the rear sight is modified so that it can be dialed down four clicks below the 6/3 setting for a 42/≅200 meter (46/≅218 yard) zero trajectory BZ.

16″ Barrel Carbine:

Zeroed at 27 meters with the 6/3 setting for a 27/300 meter zero.  The rear sight is also modified so that it can be dialed down four clicks below the 6/3 setting for the a 44/≅200 meter (48/≅218 yard) zero trajectory BZ.

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Revised Improved BZ Method — Like Santos, But Even Better:

Revised Improved Battlesight Method Philosophy:

• AR-15.com’s How To Modify Your A2 Sight For The RIBZ
  

The Revised Improved Battlesight Zero (RIBZ) is an enhanced version of the Santos Improved Battle Sight Zero (IBZ). The elevation knob on the carry handle is modified so that it will provide the same seeings as the Santos IBZ, but will additionally provide a setting for 100 yard shooting.

The rear elevation knob on a removable carry handle sight is modified so that it can be adjusted 6 clicks below “6/3” setting (“6/3 -6”), or the elevation knob on a fixed carry handle sight is modified so that it can be adjusted 3 clicks below the “8/3” setting (“8/3 -3”).  For detailed instructions on how to modify your rear sight, click on the blue link above.

Use the “6/3 -6” setting (0r “8/3 -3” with fixed carry handle rifles) for shooting at 100 yard targets.*

As with the Santos method, use the “6/3 -4” setting (or “8/3 -2” with fixed carry handle rifles) for the 50 yard/200 meter IBZ trajectory.*

As with the Army method or the Santos method, use the “6/3” or “8/3” and the “4”, “5”, and “7” settings for shooting targets at their respective distances.

Don’t expect absolute precision zeroing at every distance, but it is astonishing how well this works. Definitely read the links provided for more information on these modifications. At first it looks daunting but actually is very easy to accomplish.

* Notice that the number of clicks for the removable carry handle is double that of the fixed carry handle.

Caveats For RIBZ Technique With Other Barrel Lengths & Ammo Types:

With the RIBZ modification the rifle or carbine should be on target if the elevation knob is set to the following:

Carbine With Removable Carry Handle:

• 25 meters: “6/3”
• 50 yards/200 meters “battle zero”: “6/3 -4”
• 100 yards: “6/3 -6”
• 150 yards: “6/3 -6”
• 200 meters: “6/3 -4”
• 300 meters: “6/3”
• 400 meters: “4”
• 500 meters: “5”
• 600 meters: “6/3” after one full rotation upward

Rifle with 20″ Barrel and Removable Carry Handle:

• 25 meters: “Z” setting
• 50 yards/200 meters “battle zero”: “6/3 -4”
• 50 yards: “6/3 -4”
• 100 yards: “6/3 -6”
• 150 yards: “6/3 -6”
• 200 meters: “6/3 -4”
• 300 meters: “6/3” (or “8/3″ with fixed carry handle, 20” barrel rifles)
• 400 meters: “4”
• 500 meters: “5”
• 600 meters: “6/3”

Rifle With 20″ Barrel and Fixed Carry Handle:

• 25 meters: “8/3+1”
• 30 meters (33 yards/33 yards): “8/3”
• 50 yards/200 meters “battle zero”: “8/3 -2”
• 100 yards: “8/3 -3”
• 300 meters: “8/3”
• 400 meters: “4”
• 500 meters: “5”
• 600 meters: “6”
• 700 meters: “7”
• 800 meters: “8/3”

Splitting Hairs With Regards To The 50 Yard/200 Meter Trajectory:

The following may seem like it is unnecessarily splitting hairs, but it will help enforce the relationship between barrel length, ammunition velocity, and trajectory.  With all other variables the same, when you change barrel length then you change muzzle velocity.  If trying to achieve the same far zero, then because of the change in velocity, your near zero will be different with rifles of different barrel lengths.  The 50 yard/200 meter battle zero discussed above is technically based on a 20″ barrel rifle with M855 62-grain ammunition.  The 200 meter zero actually has different near zeros with 14.5″ and 16″ barrels.

On a 16″ barrel carbine with a removable carry handle, when the sights are dialed down 4 clicks below the “6/3” (“6/3-4”) then the sights are calibrated for a 48 yard/200 meter zero.

On a 14.5″ barrel carbine with a removable carry handle, when the sights are dialed down 4 clicks below the “6/3” (“6/3-4”) then the sights are calibrated for a 46 yard/200 meter zero.

The 46, 48, and 50 yard first zero references are presented only for technical enlightenment of the reader.  For practical purposes it is a ridiculous discussion.  When the different trajectories are compared against each other, there is only a few 100 of an inch difference between the three of them at 50 yards.  Plan on using 50 yards as your BSZ regardless of your barrel length.

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Using A2 Sights With A CMMG .22LR Conversion Kit:

• Savannah Arsenal’s CMMG Brand Conversion Kits For AR-15 Rifles
• Savannah Arsenal’s What Distance To Zero A .22LR Converted AR-15

As discussed in the first linked article, a CMMG .22LR conversion kit is great for training and plinking.  It’s the perfect way to teach rifle marksmanship to a new or young shooter.

25 Yard Zero:

As discussed in the second linked article, if you have a dedicated .22LR AR style rifle, or like to use a CMMG .22LR conversion kit in your AR, then you will find that when shooting normal velocity ammunition a 25 yard zero offers a very flat trajectory out to 100 yards.  The 25 yard zero’s trajectory provides point-of-impact withing +/- 1″ of your point-of-aim from approximately 13 yards out to approximately 80 yards, and at 100 yards a point-of-impact approximately 2.5″ below point-of-aim.With a dedicated .22LR rifle it is as simple a zeroing the sights so that your bullets impact where you aim at 25 yards.

Problems When Using Magnified Optics, Red Dot or Holographic Sights, and Backup Sights:

If you have a 5.56mm rifle or carbine that has a magnified optic, red dot or holographic sight, and backup sights, then using the conversion kit becomes a little more problematic because you can either zero the rifle for the full-size 5.56mm ammo, or zeroed for the .22LR ammo, but not both.  5.56mm ammo and .22LR ammo do not have any type of coincidental trajectories.  If you have your rifle zeroed for 5.56mm, then there are not any target distances that will share a same trajectory as .22LR.  The rifle will never be capable of hitting with .22LR where you are aiming, regardless of distance.  Look for a future Savannah Arsenal article with a possible hack to solve this problem.

What A-2 Sight Setting Provides A 25 Yard Zero?

We experimented with a 16″ barreled carbine and a 20″ barreled rifle, both flat-top upper receivers with a 6/3 removable carry handles and the traditional triangle shaped fixed front sight base.  The carbine had been zeroed at 25 meters with the “6/3” setting.  The rifle had been zeroed at 25 meters with the “Z” setting (“6/3” +2).  Surprisingly we found out that each required a different rear sight setting for a 25 yard zero with the .22LR conversion kit.

• 16″ Carbine: Use the “4” (400 meter) setting.
• 20″ Rifle: Use the “5” (500 meter) setting.

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Factors That May Cause A Rifle To Need To Be Re-Zeroed:

Many factors influence the BZO of a rifle.  If operating in a combat environment, shooters should confirm their BZO as often as possible.

To confirm zero, a shooter may begin the zeroing process by using the previously established BZO sight settings rather than placing the sights at initial sight setting.

The Following Factors Cause A Zero To Be Reconfirmed:

Maintenance: It is possible for the zero to change if ordnance personnel perform maintenance on a rifle. If maintenance was performed, it is critical that the rifle be rezeroed as soon as possible.

Temperature:  An extreme change in temperature (i.e., 20° or more) will cause the elevation zero to change. Changes in temperature cause chamber pressure to increase when hot and decrease when cold. This causes shots to impact the target high in hot temperatures and low in cold temperatures.

Climate:  Changing climates (i.e., moving from a dry climate to a tropical climate) can mean changes in air density, moisture content, temperature, or barometric pressure.  Any of these elements can affect the rifle’s zero.

Ammunition:  Inconsistencies in the production of ammunition lots can change a rifle’s zero.

Ground Elevation:  Drastic changes in ground elevation can create changes in air density, moisture content, temperature, or barometric pressure.  Any of these elements can affect the rifle’s zero.

Uniform:  If the shooter zeroes their rifle in plain clothing and then fires in full battle gear their zero will change.  The wearing of full battle gear changes eye relief, placement of the rifle in the shoulder pocket, and the way the rifle is supported on the handguard.  Shooters must establish their zero while wearing the uniform and equipment they will be wearing while engaging targets.

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Related Pages:

• Savannah Arsenal’s AR-15 / M4 Page
• Savannah Arsenal’s Tactical Rifle Essentials Page
• Savannah Arsenal’s Tactical Rifle Accessories Page
• Savannah Arsenal’s Tactical Rifle Ammunition Page
• Savannah Arsenal’s Tactical Rifle Optics Page

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