Focus on the front sight. That was initially challenging for me to get over with my first AR15. I would focus on the target and the front sight post would appear slightly fuzzy. I thought that was fast and accurate, but when it comes down to cutting hairs it is simply the improper way to utilize the peep sights on the AR15. The peep sight gives the shooter a number of advantages over open sights (such as on an AK platform).
1) The nature of peering through a small aperture limits the light exposing itself to the eye. This broadens the field of view and, in effect, gives the shooter a sharper image than what the naked eye alone could interpret. The sharpness of images in both the background (your target) and the foreground (your iron sights) increases. If you were to focus on your front sight without using the peep the the target would be completely fuzzy.
2) The nature of the peep requires it to be mounted close to the eye. Do not hamfist your rifle by mounting the peep farther from the eye that it should be. I have occasionally seen pictures of shooters mounting their Magpul (or other brand) BUIS near T5… which equates to a little less than midway down the upper receiver’s rail. Not only does this setup limit the field of view, but it also decreases sight radius and gives the eye yet another point which will fight for focus. Peeps should go near the eye.
3) The peep suppresses parallax. Yup, believe it or not, your irons sights are nearly parallax free. Peer through the small peep and you don’t need to worry about centering the front post in your viewing field… simply put it under the target and fire. Try it out: steady your rifle against a small stationary object in your home and move your head around. The front post stays underneath the object so long as you are looking through the peep. This can help in situations where speed is required to make a shot. Put the post under the target and fire.
Understanding these points will only help your shooting. The peep sight is not as stone age as some make it out to be and is by far the most accurate iron sight system around. IF you know how to use it then you can teach others how to use the sights that come with their new AR.