I have an A2 with iron sights. Nothing fancy just standard kit gun stuff. I would like to upgrade the iron sights. The apertures on the rear sight seem giant, and the front sight post could be smaller. The front sight post is an easy fix. How do I determine the best combo for say 100 yards? Even with the current small aperture, 100 yard sight picture is not 'accurate'. There are a few National Match rear sights, but how do I determine the best for my gun?