BATTLE SIGHT ZERO (BZO): Who has it right?

According to both Marine Corps and Army field manuals, achieving a proper battlesight zero is crucial to enable Soldiers and Marines to engage enemy threats without needing to adjust the elevation of their iron sights from point-blank range or zero yards/meters out to 300 yards/meters. Refer to Figure 1 for visual representation.

“In combat, your rifle’s BZO setting will enable engagement of point targets from 0–300 yards/meters in a no wind condition.”

~ Marine Corps Reference Publication 3-01A Rifle Marksmanship.

“Battlesight zero: A sight setting that soldiers keep on their weapons. It provides the highest probability of hitting most high-priority combat targets with minimum adjustment to the aiming point, a 250 meter sight setting as on the M16A1 rifle, and a 300 meter sight setting as on the M16A2 rifle.”

~ Department of Army Field Manual 3-22.9

It should be noted that the Marine Corps primarily employs yards as their unit of measurement, while the Army utilizes meters. To provide a conversion for reference, 300 yards is approximately equivalent to 274 meters, and 300 meters is roughly equal to 328 yards. In most combat situations, a battlesight zero (BZO) of 300 yards/meters is considered reasonable.

However, the Army and Marine Corps diverge in their approaches to establishing a BZO for rifles or carbines. Furthermore, various prominent shooting schools and private trainers advocate alternative methods for determining an appropriate BZO setting. Adding to the complexity, a specific special operations unit advocates and instructs a 100-yard zero. This disparity raises the questions of who is correct and which method is superior, necessitating a closer examination of the subject to dispel myths and misconceptions.

“A BZO (battlesight zero) is the sight settings placed on your rifle for combat.”

Please note that in this article, we will focus solely on discussing iron sights and reserve the examination of combat optics for a future publication.

The Stoner family of rifles and carbines has served the U.S. military and several allied forces for over four decades. Despite some challenges, these firearms have demonstrated their effectiveness on numerous battlefields worldwide. While debates may arise regarding the suitability of the 5.56mm caliber for larger targets, this article’s focus is not to address that specific argument. Instead, we will explore the most appropriate method to establish a battlesight zero (BZO) for these firearms based on specific mission parameters.

To determine the optimal BZO, we must consider the ballistics of the 5.56mm round, including both terminal performance and trajectory. Both the Army and the Marine Corps instruct that the maximum effective range of the M16A2/A3/A4 is 500 meters for engaging point targets (individual enemies) and 800 meters for engaging area targets (such as troops in the open). These parameters provide crucial context for establishing an effective BZO for these firearms.

A notable component of the Marine Corps’ known distance qualification course involves engaging stationary black ‘E’ Silhouette-style targets, commonly referred to as “B-Mod” targets. These targets measure 23.5″ wide and 39″ tall, featuring a white background, and are engaged from the prone position at a distance of 500 yards using 10 rounds. It is not uncommon for highly skilled Marines to achieve a perfect score of 10 out of 10 hits. This course serves as an excellent assessment of fundamental marksmanship skills while instilling confidence in both the Marines and their weapons.

However, it is important to acknowledge that on the battlefield, the enemy seldom remains stationary or conveniently silhouetted at known distances. Additionally, soldiers and Marines may not always find themselves in stable prone positions or behind sandbags. In asymmetric battlefields like Iraq, rules of engagement may prohibit engagement of potential combatants unless they are identified as threats. At distances of 500 or even 300 yards, it becomes challenging to discern camouflaged combatants and determine their intentions without the aid of quality optics.

Lastly, the lethality of the 5.56mm round at these extended distances must be taken into consideration. While the round’s effectiveness decreases with distance, it is essential to understand its limitations when engaging targets beyond the typical engagement range.

Let’s delve into the topic of the lethality of the 5.56mm round. Recent extensive testing conducted by the Department of Defense Subject Matter Expert Ballistics panel has shed light on this aspect. The results indicate that, apart from precise shot placement, the yawing and fragmenting effect of the round upon impact with soft tissue is the primary factor in producing lethal wounds. This effect is best achieved with a velocity exceeding 2500 feet per second, preferably above 2700 fps, for ammunition types such as M193, M855, or MK262 Mod 1.

Based on these findings, the effective range for producing lethal wounds with the 5.56mm round is approximately 200 meters when fired from a 20″ M16A2/A3/A4 rifle, or 150 meters when fired from a 14.5″ M4A1 carbine. It is important to note that this does not imply that shots beyond these ranges cannot be lethal, but rather that the probability of inflicting a lethal wound begins to decrease significantly. For instance, at a distance of 500 yards, the velocity of the 5.56mm round drops to approximately 1500 to 1700 feet per second, which is equivalent to the muzzle velocity of a .22 LR Hyper-Velocity round. While it is indeed possible to eliminate a target at that distance with a 5.56mm round, the likelihood of inflicting a lethal wound is significantly diminished beyond 200 meters.

Nevertheless, it is worth acknowledging that there have been instances where Marines and Soldiers have successfully engaged and killed enemies at distances exceeding 200 meters during recent conflicts. However, it is essential to understand that the effectiveness of the 5.56mm round decreases as the range extends beyond its optimal performance range.

Indeed, based on the findings of Department of Defense ballistics subject matter experts, it is established that the maximum lethal range for the 5.56mm round on two-legged targets is likely around 200 meters.

Regarding battlesight zero (BZO) distances, it is important to clarify that the true zeros are 200 yards, 300 yards, and 300 meters. The initial intersection points of rounds during their trajectory occur at 25 meters, 36 yards, and 50 yards. Zeroing at these shorter distances is primarily intended to get the shooter on paper and in the general vicinity of where they should be shooting at 300 meters, 300 yards, and 200 yards, respectively. However, it is still crucial to confirm and refine the BZO at those appropriate distances to ensure optimal accuracy and effectiveness.

Let’s examine the external ballistics and trajectory of the recommended battlesight zero (BZO) methods.

The Army’s recommended 25/300 Meter BZO involves zeroing the M16A2/A3, M16A4, and M4A1 rifles at 25 meters with the rear elevation set at 8/3+1, 6/3+1, and 6/3, respectively, using the small (long range) aperture. The standard requires the soldier to shoot a 4cm (1.5″) group at 25 meters, as the Army assumes that achieving this standard will enable the soldier to shoot a 48cm (19″) group at 300 meters. Once this standard is met, the rear elevation setting is adjusted to 8/3 or 6/3.

However, it is worth noting that the trajectory of the rounds does not appear to have been fully considered when the Army chose the 25/300 meter BZO. The maximum ordinate, or the highest point in the flight path, rises almost 9″ above the line of sight at around 200 meters. Following the Army’s standard for shooting groups, this would result in most shots impacting approximately 15″ above the line of sight at 200 meters. Consequently, if soldiers aim at the enemy combatant’s chest, they would end up shooting high (in the head and neck area) between 150 to 250 meters, leaving little room for windage error.

It is important to consider this trajectory characteristic and the potential impact on target engagement, especially when aiming at specific areas of the body. The 25/300 meter BZO method may require adjustments in aiming points and compensations for bullet trajectory to ensure accurate and effective engagement at various distances.

300 Meter Zero Trajectory Graph


The Marine Corps’ recommended 36/300 yard BZO is another method to consider. In this approach, the M16A2/A3/A4 and M4A1 rifles are zeroed at 36 yards with the rear elevation set at 8/3 and 6/3 using the small (long range) aperture. This results in a trajectory with a maximum ordinate of slightly over 4.5″ above the line of sight at around 200 yards.

With the Marine Corps’ standard of achieving 12″ groups at 300 yards, most rounds would impact approximately 9″ above the line of sight. When aiming at the enemy’s chest, the rounds would land high on the upper chest just below the neck between 150 and 200 yards. This BZO provides a slightly better margin for error on the part of the shooter compared to the 25/300 meter zero method.

By allowing a bit more room for error in elevation adjustments, the 36/300 yard BZO may offer some advantages in terms of accuracy and effectiveness. However, it is important to note that adjustments to aiming points and consideration of bullet trajectory are still necessary for precise target engagement at various distances.

300 Yard Zero Trajectory Graph


The 50/200 yard zero is indeed a commonly used BZO among many reputable shooting schools and instructors across the country. This zeroing method involves zeroing rifles and carbines using the large (0-200) apertures with the rear elevation set at 8/3 or 6/3.

The 50/200 yard zero offers a very flat trajectory, with a maximum ordinate of just over 1.0″ between 50 and 200 yards. When aiming at the center mass of a target with a 12″ standard at 300 yards, it can be expected that most rounds will impact within 4 to 5 inches from the point of aim out to 250 yards. Beyond that distance, the trajectory drops relatively quickly, with rounds impacting approximately 6″ below the line of sight, accounting for shooter error, and up to 12″ below with significant shooter error at 300 yards.

However, even with a 12″ drop below the center of the chest at 300 yards, the rounds would still impact in the blood vessel-rich lower abdomen and groin area. This provides more leeway for windage errors and still maintains the potential for effective engagement.

The 50/200 yard zero offers a compromise between a flat trajectory for close-to-mid-range engagements and sufficient terminal ballistics for effective hits on vital areas of the body. It allows for a relatively forgiving margin of error in windage and still delivers rounds where they can cause significant damage to the target.

200 Yard Zero Trajectory Graph


The 100 yard zero is indeed a less common BZO but is specifically utilized by an elite U.S. military special operations unit to align with their unique mission requirements. This particular BZO is tailored to their operational profile, which often involves performing direct action missions that demand highly precise shots on threats within 100 yards. Additionally, they must swiftly transition to close quarter battle actions inside confined spaces.

The 100 yard BZO proves effective for threat engagements within 200 yards, providing accurate and reliable hits. However, it’s important to note that the trajectory of rounds drops off rapidly beyond that distance. As a result, the 100 yard zero is not optimized for engagements at longer ranges, as the rounds will experience significant bullet drop and diminished accuracy.

The choice of the 100 yard zero reflects the specific needs and objectives of this elite special operations unit, where precision and rapid target engagement at close to mid-range distances are of paramount importance.

An interesting observation is brought up regarding the Army and Marine Corps Technical Manual for the M16A2, which suggests that zeroing the rifle at 300 yards or meters using the small (long range) aperture and then flipping to the large (0-200 short range) aperture would result in a 200 yard/200 meter zero. However, when testing this theory, it was found that the two zeros were not the same.

In the field test, it was discovered that the large aperture shot groups were 6″ low and 3″ to the right at 50 yards. Extrapolating this information to 200 yards, it would mean that the shot groups would be 24″ low and 12″ off to the right. This discrepancy implies that shooters would completely miss their intended targets.

While the difference in elevation between the small and large apertures was expected due to the misalignment of their centers, the shift in windage was an unexpected observation. It was found that when the rear aperture is rotated from small to large, it moves slightly to the right due to the threaded screw mechanism of the rear aperture sight. This shift in windage results in a corresponding shift in the impact of the rounds to the right.

These findings highlight the importance of understanding the mechanical aspects and potential discrepancies when zeroing a rifle using different apertures and distances. It emphasizes the need for practical field testing to validate theories and ensure accurate shooting performance.

Top group was shot at 36 yards with M855 5.56mm NATO ammo with the Small (long range) Aperture and the bottom group was shot with the same ammo and rifle at 50 yards with the Large (0-200 short range) Aperture.

The choice of the best BZO depends on various factors such as mission requirements, the nature of the enemy, the characteristics of the terrain, and the specific context of the engagement. In the author’s opinion, the 50/200 yard zero is the preferred choice. For civilians or law enforcement officers, zeroing with the large aperture at 50/200 yards and leaving the sights unchanged is recommended, as most defensive or offensive shots within their scope of operation will likely be within 200 yards.

However, for infantrymen operating in open mountain ranges like Afghanistan, the 36/300 yard zero with a small aperture may be more suitable. This allows for more precise shots at longer distances, with the option of switching to the large aperture within 100 yards for close-quarter engagements, such as clearing small villages.

In urban environments like Fallujah or Baghdad, where engagements are typically at shorter ranges, the large aperture zeroed at 50/200 yards would be preferred.

Ultimately, soldiers and Marines should gather information and stay informed about current and valid Tactics, Techniques, & Procedures (TTPs) to make well-informed decisions based on their specific circumstances. Each individual must make decisions based on their own judgment and unique context.

figure 1

U.S. Army TM 9-1005-319-10/USMC TM 05538C-10/1A

When battlesights are on your rifle:

a. The front sight post and rear sight windage knob are adjusted so you can hit your point of aim at 300 meters.

b. The unmarked aperture must be in the up position.

c. The 300-meter mark is aligned with the mark on the left side of the receiver.

M16A2/3/4, M4, and M4A1 weapons. The unmarked aperture is used for zeroing and target engagement at all distances on the KD range. When engaging targets beyond 300 meters the windage knob should be adjusted to the range of the target. 400-meter targets are engaged on the setting 4 flush and 450-meter targets would be set on 4 plus two clicks.

3.  Basic training soldiers will only zero on the 25-meter range.

FM 3-22.9


The creed of a United States Marine
Maj. Gen. W. H. Rupertus, USMC

This is my rifle. There are many like it, but this one is mine.
My rifle is my best friend. It is my life. I must master it as I must master my life.
My rifle, without me is useless. Without my rifle, I am useless. I must fire my rifle true. I must shoot
straighter than my enemy who is trying to kill me. I must shoot him before he shoots me. I will…
My rifle and myself know that what counts in this war is not the rounds we fire, the noise of our
burst, nor the smoke we make. We know that it is the hits that count. We will hit . . .
My rifle is human, even as I, because it is my life. Thus, I will learn it as a brother. I will learn its
weaknesses, its strength, its parts, its accessories, its sights, and its barrel. I will ever guard it
against the ravages of weather and damage. I will keep my rifle clean and ready, even as I am
clean and ready. We will become part of each other. We will …
Before God I swear this creed. My rifle and myself are the defenders of my country. We are the
masters of our enemy. We are the saviors of my life.
So be it, until victory is America’s and there is no enemy, but Peace!

figure 2

U.S. Army TM 9-1005-319-10/USMC TM 05538C-10/1A


a. Rotate the elevation knob down to the 300-meter mark.

b. Flip the unmarked aperture down and use the larger aperture marked “0-2.”

NOTE:  The 0-2 aperture is preset for targets between 0 and 200 meters. Moving targets at close ranges are easier to hit if you use the larger aperture.
Sgt Dean Caputo, Arcadia CA PD, Colt Armorer Instructor, and Gunsite Range Master shooting an M16A3 on the Arcadia PD’s excellent 50 yard indoor training range.  He was kind enough to assist us during this testing, as well as allow us to use his department’s facilities.

This is an updated version of an article original published in August 2008 for SWAT Magazine By LtCol Freddie Blish, USMC (Ret), the General Manager of ROBAR Companies, Inc and a Range Master at Gunsite Academy, Inc.

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