You can still see the front sight (most of it anyway), but it takes a little longer to pick it up. Also if you have a GB with the winged front sight you have to make sure you're looking at the front blade and not one of the side wings. I currently have an Aimtech Scout Rail on mine, and its the same deal, you're looking at the front sight through a tunnel. I painted my front sight blade with flourescent red paint to make it easier to pick up-it helps alot.