Quote Originally Posted by Cobrasks View Post
Excellent thread .

Of specific interest to me was how this representation
really shows how the impacts at various ranges get closer
with heavier bullets in a 16 inch barrel .
Specifically with the 50 yard zero .
I'm still in the 50 yard zero camp for Aimpoints .
I've considered the 100 yard zero many times but
keep coming back to the 50 .

Does any one have the math as to how much the
impacts are changed with an optic versus irons ?

Specifically for Aimpoints with a lower 1/3 co-witness
as they would be slightly further from the barrel .
It's pretty much not a factor.
Here's an example:
2700 f/s M855
200 meter zero
2.5" LOS over bore (iron sight height):
50 meter impact: .63" high
100 meter impact: 1.96" high
3" LOS over bore (optic too high to cowitness):
50 meter impact: .25" high
100 meter impact: 1.71" high

As you can see, the closer zero magnifies the effect of the sight height difference, and even then, the difference is negligible.
For reference, with AR pattern rifles, top of rail is right around 1.2 inches above bore.
A rail-mounted front sight will be between 1.2 and 1.5 inches above the rail (depends on how far in/out it needs to be to achieve zero).
Ballistic calculators use the distance between the line of sight and the muzzle (this will be important in a second).
The sight offset is therefore 2.4-2.7 inches over bore. I usually use 2.5 inches for iron sights.
A standard height 1.5 inch optic base generally gives a 2.6-2.8 inch height, depending on tube thickness, once zeroed.
Lower 1/3 cowitness sights are usually 1.6 inches above rail (to center of glass), for 2.8, but it's a little less at the muzzle.
A NVG height non-cowitnessing sight will be about 1.9 over rail, for a 3.1 inch offset, closer to 3 at muzzle.

For simplicity, I use the following:
Irons and absolute cowitness optics: 2.5"
Lower 1/3, and optics in standard 1.5" mounts: 2.7"
NVG Height/High Mounts: 3.0"

And really, if you're using a 100 yard/meter or further zeroing concept you can just use 2.7 across the board and be just fine out to 1,000 meters without having data confliction.