Revised Improved Battlesight Zero
The standard A2 rear sights on an AR-15/M16A2 were designed with elevation settings for 300 to 800 meters. The Santose Improved Battlesight Zero allows for an elevation setting of 50 yards/200 meters for one of the most all-around useful trajectories obtainable with the 5.56mm/223 Remington cartridge when fired from an AR-15.
Neither of the above sighting schemes allow for an elevation setting giving you point of aim equals point of impact at 100 yards. Since 100 yard shooting ranges are some of the most commonly found ranges in the United States, it would be useful to have such a setting on our AR-15s. This can be achieved quite easily with nothing more than a 1/16” allen wrench. It’s really just a matter of taking the Improved Battlesight Zero one step further.
There is a witness hole on the A2 rear sight base that gives you access to the index screw that you will need to loosen with the 1/16” allen wrench to make the necessary alteration to the elevation drum. The witness hole lines up with the index screw only when the elevation drum is set to 8/3. Set your elevation drum on the 8/3 setting and turn the screw counter-clockwise 3 to 4 complete turns. You don’t want to remove the screw. You want to loosen it enough to allow the elevation index wheel (the top part of the elevation drum with the numbers on it) and the elevation knob (the bottom part of the elevation drum) to separate and be able to move independently of each other.
Once you have loosened the index screw, use one hand to hold the allen wrench in place on the screw and with your other hand turn the elevation knob (the bottom part of the elevation drum) 4 clicks clockwise.* You should see the rear sight base moving up while you do this. The elevation index wheel should not move while you are doing this. (We really only need to turn the elevation knob 3 clicks clockwise, but by turning it 4 clicks we get a “buffer zone” that keeps the rear sight base from coming into contact with the lower receiver when the sight is moved to the lowest used setting. This gives you a more consistently repeatable sight setting.)
Now that you have moved the elevation knob 4 clicks clockwise, taking care to make sure the elevation index wheel has not moved, firmly tighten the index screw. Starting with the elevation drum at the 8/3 setting, you should easily be able to turn the drum counter-clockwise 3 clicks and see the rear sight base moving down. (You should be able to turn the elevation drum one more click counter-clockwise for our “buffer zone.”) You are now ready to head to the shooting range.
As I mentioned earlier, this sighting scheme is really just taking the Improved Battlesight Zero one step further. Starting with the elevation drum at the 8/3 setting, turn the elevation drum counter-clockwise 3 clicks (8/3, -3). This is your 100 yard point of aim equals point of impact setting. From a distance of 100 yards, zero the rifle with the rear sight at this setting (using the small sight aperture). Do not change this rear sight elevation setting while zeroing. Use the front sight post only to make changes in elevation while zeroing.
The beauty of the RIBZ sighting scheme is that once you have zeroed the rifle with this method, you will have your 100 yard zero setting and the other settings of the elevation drum remain intact (within the limits of the coarse adjustments of the A2 sights). If you want to use the Improved Battlesight Zero, simply set the elevation drum to 8/3, -2 and you're good to go. To use the standard military 300 meter setting, just set the elevation drum to 8/3. You can also start the zeroing process by obtaining the Santose Improved Battlesight Zero at a distance of 50 yards with the rear sight on the 8/3, -2 setting. Obviously, slight variations will be encountered depending on the ammunition used and the actual amount of movement with each click of the various sights. The results will certainly be close enough “for government work.”
When using this sighting method, you may find that once you have set your 100 yard zero, the top of the base of the front sight post is now slightly above the top of the well in the front sight base. If this happens, the “0.040” taller” front sight post from Bushmaster provides a quick and inexpensive fix.
100 yard zero (8/3, -3)
Improved Battlesight Zero (8/3, -2)
Standard 300 meter zero (8/3)
All click references should be doubled when using detachable carry handle sights.
IBZ (6/3, -4)
While the Revised Improved Battlesight Zero is certainly not perfect, here is an example of how well it does work at the distances typically encountered at the public KD ranges in my state. I zeroed my 20” Colt HBAR with A2 sights at 100 yards as described in this thread. Here is a pic of a 10-shot group from 100 yards.
100 yards, (8/3, -3)
Next, I packed up my gear and headed to the 50 yard line. By simply coming up one click on the elevation wheel (8/3, -2), I was in the 10-ring at 50 yards.
50 yards, (8/3, -2)
Lastly, I moved down to the 25 yard line. With this sighting scheme, setting the elevation wheel to (8/3, +3) [or (8/3, +2) depending on the rifle] gives me the necessary elevation for 25 yards. (Again, due to the course adjustment of the AR-15 sights and manufacturing tolerances none of these settings are perfect.) In fact, if you don't have access to a 100 yard range or you just want to “get on paper” before heading to the 100 yard range to refine the zero, you can zero at 25 yards using this setting.
25 yards, (8/3, +3)
Here is a down-loadable target in .pdf format that can be used for zeroing 20” uppers with A2 sights at 100 yards using the Revised Improved Battlesight Zero. The dashed vertical grey lines represent one click of the windage knob. The dashed horizontal lines represent one click of the FRONT SIGHT POST.
100 yard zeroing target
When printing, you need to have the “page scaling” option in Adobe Reader set to “none” in order for the target to print with the correct dimensions.
continued . . .