Here's the starting position when zeroing an M16A1: 1. Bring the rear sight all the way to the left; 2. Turn the rear sight seventeen (17) clicks to the right. 3. The front sight base should be flush on the base of the sight assembly. 4. Turn the front sight base eleven (11) clicks down. Note: use the rear aperture with the L when zeroing. This is the starting position. Fire three rounds, and make the necessary correction(s). Fire another three and correct if necessary. The maximum no. of rounds needed to zero your M16 this way won't be over 20 rounds. Got this from the US Marine Manual.