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Alright, alright, alright, let's talk about some common rifle zeroes. Please keep in mind that these blogs are my opinions and do not reflect any negative connotations to any agency. Now that all that crap is out of the way, what is a rifle zero and what are some common zeroes utilized by various agencies. Please also keep in mind that we will bash the zeros I don't like in later Blogs :)
Let us first discuss how the zero works. The rifle zero is accomplished by moving the rifle optic, or iron sights, up/down (elevation), and left/right (windage) to coincide with a specific ammunition's point of impact (POI). Once you have your rifle zero, given the specific ammunition, the shooter can now attain point of aim (POA) and point of impact (POI) accuracy. In short, this means that the bullet will impact where I put my sights. There are some serious underlying factors to take into account when zeroing the rifle, but we will address those in future posts. Keep it simple slick.
There are many different Battlesight Zero (BZO) schools of thought throughout the shooting communities. For example, the US Army has adopted a 25 meter zero. The US Marine Corps utilizes a 36 yard zero. Different agencies have stuck with a 50 meter zero. Finally, there are other units/agencies out there that use a 100 meter BZO. Each of these zeroes have unique pros and cons, and each zero has been adopted with certain "end users" in mind. To expand, given the trajectory of the NATO 5.56, M855 Ball rifle round, each service/agencies utilizes their respective BZO's to accomplish their goals.
Now let's turn up the confusion. Again, given the trajectory of the 5.56 round, the 25, 36 yard, and 50 meter zeroes are actually only the "initial zero". The advertised "true zero" for the 25 meter standard is 300 meters. How in the world is that accomplished and what am I raving about?! Imagine your favorite quarterback, Deshaun Watson, throwing a National Championship winning touchdown pass to wide receiver Hunter Renfrow (Go TIGERS!). The football and the rifle round are extremely similar. The rifle round leaves the muzzle in much the same way it leaves the quarterback's hand. The round then spirals upward and drops into the target. Now imagine that our quarterback could throw the football 450 meters. As the quarterback looks with his eyes (the rifle optic or iron sights), he launches the football (bullet leaves the muzzle of the rifle travelling forward and slightly upward). As the football travels toward the intended target, there will be a point in the trajectory where the football intersects with the line of sight of the quarterback. This is our 25 meter, initial zero. What comes up, must come down right? The football reaches the peak of its trajectory and begins to fall. At the 300 meter mark, the football will again intersect with the quarterback's line of sight. That 300 mark is the true zero. Similarly, the 36 yard zero for the Marine Corps maintains the same initial concept with a true zero at the 300 yard line. The 50 meter zero has a 200 meter true zero following the same school of thought.
What about the oddball? The 100 meter zero is a little bit different. For shooters looking to accurately engage targets out to 400 meters, with 5.56, the 100 meter may be the "chosen one". The 100 meter zero has only place where the round intersects with the optic/iron sight line of sight. In other words, the "true zero" is achieved at the max height of the bullet trajectory. This means that, at 100 meters, the shooter has both point of aim and point of impact. Certain units found that the 100 meter zero was the best choice given engagements out to 400 meters with 5.56 caliber rifles. For targets inside of 100 meters, compensate for sight to boreline offset (the roughly 2.5 inches between the barrel and the rifle optic/iron sight). For targets in the 200 meter range, aim/hold the sights 2 inches high. 300 meter engagements require a 1 foot hold over the target. Finally, 400 meter targets require a 2 foot hold over the intended target. The "point target", maximum effect range for 5.56 is only 450 meters with an M4 anyway. Therefore, in my opinion, anything past 400 meters, depending on the objective/mission, requires a larger caliber. Anything with 400 meters is easily, and accurately engageable.
In future blogs, we will discuss the misconceptions and problems with the 25 meter, 36 yard, and 50 meter BZO's.