Is there and RIBZ procedure for an M16A1? I know the 25M  procedure in the TM has you use the L aperture, but which aperture do you use at 50yds for the RIBZ?

A1 elevation is adjusted on the front sight post.

When you say to use the "small aperture", I assume you mean the unmarked one. If I do zero at 50yds with the unmarked aperture, do you know hat flipping to the L marked aperture will do?

I guess what I am wanting to know is if I sight in with the unmarked aperture at 50 yds, I should be zeroed for 50 and 200 yds. If I then flip to the L aperture, what am I zeroed for now?

When I was in the Marine Corps using the A1 BZO was 11 /17. The elevation was set 11 clicks down into the front site base and for windage you turned the rear aperture all the way to the right starting at mechanical zero then back 17 clicks to the left. That was battle site zero. You used the unmarked aperture up to 300yrds and the marked aperture shooting over 300yds. For qualification purposes shooting standing, kneeling, sitting and prone your dope would change shooting from the 200, 300, and 500 yd line. It's been about 35yrs since I last qualified with the A1. Please correct me if I am wrong. BZO was intended for combat situations to shoot at any distance by any given Marine.