AR-15 Sights and the ‘Z’ Notch

As I was perusing the Army’s new Rifle & Carbine Marksmanship Manual, TC 3-22.9, I noted something interesting about the iron sight description. On page 3-9, the description of the iron sight, it mentions that the sight’s elevation should be set to the 300 setting plus one click up for a 25 meter zero.

This got me thinking about my post on the Revised Improved Battlesight Zero (RIBZ) from way back. It also brought to mind some things I didn’t account for back when I first got started, namely the ‘Z’ setting on the carry handle rear sight.

Z setting

On a detachable 6/3 style sight (the most common today), this “Z” setting is two clicks above the 6/3 marking. On the older 8/3 sight, it is one click up. What exactly is this setting for, you ask? Well, if you haven’t figured it out, the “Z” stands for “Zero,” particularly at 25 meters. However, whether or not you use the setting depends on the configuration of your rifle.

You see, due to the higher velocity and longer sight radius involved with a 20″ rifle barrel, the angles involved in sighting devices are slightly different than with a shorter M4 Carbine. Since the detachable 6/3 sight gets used on both the carbines it was developed for as well as the M16A4, a compromise had to be made. Traditionally, if used on a M4, the sight was left on 6/3 for a 25 meter zero. If used on a rifle, the sight was clicked two notches up to the “Z” for a the same distance. Once zeroed at 25 meters (for a rifle), the sight was clicked back down to 6/3 and confirmed at 300 meters. That is something I left out of the original RIBZ post, and I will probably go back and add it.

Of note, the new marksmanship manual appears to “average” the two different procedures and tells the user to click one notch up, right in between “Z” and the 6/3 setting for both carbines and rifles. Interestingly, for the MaTech BUIS, 3-22.9 says to zero a M16 on the white line, while a carbine should be left on the 300 setting. I cannot say the reason for this difference, but it is interesting.

As for me, I will continue sighting the Musket in at 25 meters using the “z” whenever I use the carry handle sight (which, honestly, isn’t very often these days).

1 thought on “AR-15 Sights and the ‘Z’ Notch”

  1. As an alternative – one can use the 6/3 setting and zero at 36 yards with the “musket.” You’ll be zeroed correctly. This trick works with 20″ barrels and also with 18″ barrels. This trick works with milspec ammo (M193 and M855) and the drops are accurate to within 1 MOA out to about 500.


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