A BZO (Battlesight zero) is the sight settings placed on your rifle for combat. 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
Or
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
Per both the Marine Corps and Army field manuals, a proper Battle-sight zero will allow a Soldier or Marine to engage an enemy threat without adjusting the elevation of their iron sights from point-blank range or zero yards/meters out to 300 yards/meters. See Figure 1 at the end of this article (excerpt from U.S. Army TM 9-1005-319-10/USMC TM 05538C-10/1A). Note that the Marine Corps teaches and uses yards and the Army teaches and uses meters. For edification, 300 yards is roughly 274 meters and 300 meters is roughly 328 yards. A 300 yard/meter BZO makes sense for most combat situations. However, the Army and Marine Corps differ in how to set a BZO on a rifle or carbine. To add even more confusion, numerous well-known shooting schools and private trainers teach a different method for placing a proper BZO setting. Additionally, a certain special operations unit advocates and teaches a 100 yard zero.
Who is right? Which method is best? Why?
To answer these questions and others we need to address some of the myths and misconceptions floating around regarding the proper Battlesight zero to place on a Soldier’s or a Marine’s M16A2/A3/A4 Rifle or M4A1 Carbine iron sights. We are only going to address iron sights in this article and save a look at combat optics for a future issue.
The Stoner family of rifles and carbines have been with the U.S. military and some of our allies for over 40 years. While not without its problems, it has proven itself worthy on numerous battlefields around the world. Some may argue that the 5.56mm caliber is inadequate for large two-legged critters, but the purpose of this article is not to address that point. Instead consider what might be the best method to BZO these firearms given a particular mission parameter.
We need to consider the ballistics, both external and terminal, of the 5.56mm round in relation to a proper BZO. Both the Army and the Marine Corps teach that the maximum effective range of the M16A2/A3/A4 is 500 meters on a point target (individual enemy) and 800 meters on an area target (i.e. troops in the open). Part of the Marine Corps’ known distance qualification course is engaging a stationary black ‘E’ Silhouette style (human-shaped) targets, called “B-Mod,” 23.5” wide and 39” tall on a white back ground with 10 rounds at a distance of 500 yards from the prone position. It is not uncommon for Expert rated Marines to hit 10 out of 10. This is a great test of basic marksmanship. It also provides Marines with confidence in themselves and their weapons. However, on a battlefield seldom does the enemy remain stationary or perfectly silhouetted at a known distance, nor is the soldier or Marine always in a stable prone or sand-bagged position. Also, on an asymmetric battlefield, like Iraq, the rules of engagement may not allow you to shoot at a potential combatant if you can’t identify that they are a threat. 500 yards or even 300 yards is a long distance to pick out camouflaged combatants, as well as determine their intentions, without a quality optic. Finally, we have to consider what the lethality of the 5.56mm round is at those distances.
Let’s look at the lethality of the 5.56mm round first. Extensive testing done by the Department of Defense Subject Matter Expert Ballistics panel recently concluded that besides proper shot placement, the biggest aspect of producing lethal wounds was the yawing and fragmenting effect of the round when it impacted soft tissue. This requires a velocity above 2500 feet per second, preferably above 2700 fps, for M193, M855, or MK262 Mod 1 ammo. This equates to a lethal range of approximately 200 meters with a 20” M16A2/A3/A4 rifle or 150 meters with a 14.5” M4A1 carbine. That is not to say that a shot beyond that range will not be lethal, only that the probability begins dropping dramatically. As an example at 500 yards the velocity of the 5.56mm rounds is approximately 1500 to 1700 feet per second, which is equivalent to the muzzle velocity of a .22 LR Hyper-Velocity round. Again, can you kill someone at that distance with a 5.56mm round? Yes. There have been Marines and Soldiers who have done so during our recent conflict at that distance. However, the likelihood of inflicting a lethal wound with a 5.56mm round is significantly diminished past 200 meters.
Okay, so DOD ballistics SMEs have established that 200 meters is probably the maximum lethal range for the 5.56mm round on two-legged critters. Also, keep in mind that the BZO distances of 200 yards, 300 yards, and 300 meters are the true zeros. 25 meters, 36 yards, and 50 yards are just the initial intersection of rounds during its trajectory. Zeroing at 25 meters, 36 yards, and 50 yards is only to get you on paper and close to where you should be shooting at 300 meters, 300 yards, and 200 yards respectively. You will still need to confirm and refine your BZO at those appropriate distances.
Now let’s look at external ballistics and trajectory of the various recommended BZOs.
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