tazfootball2, if you haven't done so already, take a look at the zeroing tips on the Aimpoint website: Aimpoint : How to zero your Aimpoint sight
Warning: If you are easily confused and/or have OCD-type tendencies to over-think/over-analyze things way beyond regular human reasoning, do yourself a favor and skip the following paragraph, and go straight to 'After excessively pondering...'.
I have long been a fan of iron sights on rifles. While I am not entirely new to the AR platform, I am new to using optics on the AR. I've recently acquired a red dot optic and have been reading various different methods on how to zero it. I got somewhat wrapped up in the fact that a 1x optic that has a lower 1/3 co-witness with the iron sights has a higher sightline over bore than the irons with the dot centered in the optic. Because the centerline/sightline of an optic with a lower 1/3 co-witness is higher over bore, the ballistics chart that Nguyen posted - assuming the chart applies the the iron sights - would theoretically be slightly off. Basically speaking, the centerline for the optic with a lower 1/3 co-witness is higher over bore than the irons, therefore the bore would need to be pitched upwards ever-so slightly to match the irons 50yd POI/zero. As a result, POI between the Aimpoint/1x optic should in theory be off of the irons POI at 200yds. Not by much, but off nonetheless. In theory.
After excessively pondering all that theoretical crap, I snapped out of the mind-boggling fog I was in and realized that the iron sights and the Aimpoint/Red dot/1x optic with a lower 1/3 co-witness are two completely separate sighting systems on the same weapon, and both should zeroed independently of each other. That's my thinking, and I'm going to stick with it.
Based on the reading I've done, here's how I plan to zero my lower 1/3 co-witness 1x red dot optic:
-Zero the optic to POI at 50 yards.
-Check zero at 200 yards. POI and POA should be pretty close. Fine tune as needed.
-Verify zero again at 50 yards, but DO NOT ADJUST. Adjusting the optic at this point will throw the 200yd zero off.
-Shoot at 100 yards, note where POI is in relation to POA. Again, DO NOT ADJUST the optic.
Other things to consider:
-Try to use the same type ammo when zeroing.
-Use the red dot at its lowest visible brightness setting for you when zeroing. It is said this will produce more accurate results.
Sorry for the excessive crippity-crap. I hope it helps you, anyways.