First of all, I apologize if this is too elementary, I mean no offense i just don't want to presume, and miss effectively communicating.
It makes sense that the rounds are high at 100,
since you have set a 300 yd zero,
they have to still be going up at 100 so that the will be coming down at 300.
A rule of thumb with the 223 in the AR is that a round crosses the line of sight twice,
once on the way up and once on the way down, at about 25 and 250 meters
let's see if I remember correctly...
the 8/3 is the setting for battlefield zero at 300 meters (which is the same notch on the knob as for 800 meters if rotated around).
rotate the elevation knob one click up (right) from 8/3 for zeroing at 25 yds
Now according to the Marine Corp manual (PARAPHRASED):
Do not move the front post it should be very close as set at the factory
center the rear sight mechanically in the carry handle
set the unmarked aperture up (=smaller one)
(the larger aperature is marked 0-2, not that one)
the elevation knob should be one click above 8/3 as above
fire a group,
to raise the group rotate the front post clockwise
to move the group right turn the windage knob clockwise
you are now zeroed for 300 meters
use the larger aperature marked 0-2 for engaging targets at night, in dense jungle or at closer distances than 200 meters.
And in the setting of infantry, tho the rounds may impact slightly high, you will still hit the big part. Remember when you fire on the torso, you aim for the middle of the torso, not the presumed place of the pericardium. So rather than the rounds striking just below the sterum (with perfect aim/placement) at under 300 yds they impact between the sternum and the neck. It's not perfect, but it's also not intended for bench type shooting.
Whew! now that is done, if you plan to use you AR 15 for mostly CQB shooting, for instance on an entry team, you may desire a different type of zero.
Because of the mechanical offset of the sights from the barrel you need to select the point of aim = point of impact which you desire.
And realize you wil need to compensate:
AS YOU APPROACH THE TARGET YOUR ROUNDS WILL STRIKE LOW,
because of this offset.
On my AR 15 I have my point of aim = point of impact at 25 yds; other options would be at 50 or 100 yds.
So I am not confused, I have a red dot (reflex trijicon) which is set point of aim = point of impact at 10yds and at very close distances (inside a bldg) i use the red dot and ignore the iron sights; that way I don't have to mentally compensate for the mechanical offset.
I hope that helps
Doc
please feel free to email me for further info if you want
