The AR-15 rifle has two adjustable sights- front and rear. Zeroing elevation adjustments are made using the front sight, and windage adjustments with the rear.
The rear sight has an elevation knob with range indicators from 300 to 800 meters and two apertures for range. One aperture is marked 0-2 for short range from 0-200 meters and the unmarked aperture for normal range from 300 to 800 meters. This unmarked aperture is used in conjunction with the elevation knob for 300-800 meter targets.
The rear sight also consists of a windage knob on the right side of the sight. Each click of the windage knob will move the strike of the round from 1/8 inch at 25 meters to 4 inches at 800 meters. A windage knob pointer is on the windage knob.
The front sight consists of a rotating sight post with a spring loaded detent. This detent can be depressed using a sight adjustment tool, or using a sharp point such as a cartridge tip.
The following procedure will establish a zero at 25 meters, and your AR-15 will be set with a 300 meter battlesight zero. This means that all shots will be within a 9" circle at all ranges up to 300 meters.
Establish Mechanical Zero -
Align the windage indicator mark on the 0-2 aperture with the center line of the windage scale (the unmarked aperture is up)
Rotate the elevation knob down until the range scale 8/3 (300-meter) mark is aligned with the mark on the left side of the receiver.
Rotate the front sight post up or down as required until the base of the front sight post is flush with the top of the sight post well.
Carefully aim and fire each shot of a 3-shot group at a paper target set up at 25 meters. If your shots are not striking the point-of-aim, then adjust your sights.
To raise the next shot group, rotate the front sight post in the direction marked UP (clockwise)
To lower the next shot group, rotate the front sight post in the direction marked DOWN (counter-clockwise)
To move the next shot group left, turn windage knob counterclockwise
To move the next shot group right, turn the windage knob clockwise
Continue to fire 3-shot groups and adjust the sights until you have a tight group at the point of aim.
Once this is done, the unmarked aperture is automatically zeroed. Rifle is now combat-zeroed all other ranges on the elevation knob are also zeroed, so to engage target at say 500 meters, turn wheel to 5.
The front sight consists of a square, rotating sight post with a four-position, spring-loaded detent. The front sight is only adjusted during the initial zeroing procedure and then it isn’t ever manipulated again. In the zeroing process discussed further down this page it states that the sight is initially set at the mechanical zero position (as seen in the photo to the right) where the flange at the base of the front sight post is flush with the top of the front sight tower.
Beginning with the rear sight on the correct setting for the zeroing process, the front sight is raised or lowered to move the shot group up or down until the rounds are impacting at the correct point. At that point the sights are considered calibrated and any range changes are made with the rear sight drum.