I sighted in my Colt Lightweight Sporter per the factory manual instructions for a 25 meter range using the small diameter aperture. When I switch from the small diameter aperture to the large diameter aperture I am printing about 5 inches low on the same 25 meter range. Windage is OK for both settings. Has anyone ever encountered or heard of this problem? Any info on this subject would help. Thanks in advance.  

Quoted: It took a few days to piece the puzzle together but here's what I'll eventually do to produce the "perfect" 200 yard AR-15 rifle: (1) Install a "same plane" aperture sight, which will preclude the necessity to crank up or down when switching apertures. (2) Sight-in at 50 yards using the Improved Battlesight Zero method. Life is much simpler with a MINI-14. Only one aperture size to worry about and only one elevation adjustment to worry about. Sight in at 50 yards and your done. However, once the AR-15 is sighted in using the above method, you have a choice of two apertures and calibrated capability to extend sight range from 200 meters to 800 meters.

You are absolutly correct, the Mini-14 has the advantage over the AR, please email and I will properaly dispose of that nasty firearm for you.

MillerSHO,

You are right after all. My MINI-14 doesn't have any advantage over my AR. Reason is my MINI-14 has a folding stock and my AR doesn't.

Quoted: It took a few days to piece the puzzle together but here's what I'll eventually do to produce the "perfect" 200 yard AR-15 rifle: (1) Install a "same plane" aperture sight, which will preclude the necessity to crank up or down when switching apertures. (2) Sight-in at 50 yards using the Improved Battlesight Zero method.

You came to the same conclusion that I did a couple of years ago.  I set up my patrol carbine with the Ashley rear sight and I usually use the smaller of the two apertures.  I had also tried out their big dot front sight, but found the post to be too wide for my needs.  I'm still surprised that Ashley (as far as I know) is the only manufacturer to offer the same plane design.

Eric,

Thanks for the info. I will eventually install the Ashley same plane aperture sight. I believe the Ashley small aperture is .100, compared to the AR-15 small .050 aperture. The .100 aperture would be much more to my liking for a less than 200 yards anticipated usage. Right now I have the AR set to the 200 meter IBZ, with the exception that I didn't slip the calibrated elevation knob back 2 clicks under the 300 meter setting. That is, I left the elevation knob at the 300 meter setting and sighted in the small aperture for a 50 yard zero (equivalent to a 200 yard zero). With this setting, I find I have to set the elevation to 1 click past 500 meters to obtain same point of impact with the large aperture.