Here are the deets on adjusting your sights for the 25/300 meter zeroing for M 4 and M 16 style ARs.
Shamelessly ripped from the internet.
To achieve a 25/300 meter zero for your AR-15, follow these detailed instructions.
Hang the target so that the center cross is at the shooter’s eye level. For best results, shoot from a benchrest.
Set the rear sight to the appropriate position for your rifle model. For M4-style sights, turn the rear sight to the “8/3” position. For M16A2 and M16A3 sights,
turn up one click past “8/3”. For M16A4 sights, turn up two clicks past the “6/3” setting to the “Z” mark.
Hang the target at 25 meters. Fire precise, three-shot groups at the center dot and adjust your sights according to the targets above. This gives you a battle-zeroed rifle out to 300 meters
And this hack will amaze you! Simply aim at the belt buckle of any ‘target’ out to 300 meters. The round will impact there at 25 and 300. In between it will rise up the torso. At 400, aim at the head and gravity will get you a center of mass hit.
KatNap Fever! 