Iv'e been staying out of this thread since there are so many people here who shoot better than I do, but just want to reinforce something kraigwy just said; blanking one eye but keeping both open delays eye strain and helps focus.
I use one of these
http://champchoice.com/store/Main.as...ns&item=CC100W and, even though I can not see through the translucent plastic, when it feels to me like both my eyes are focused on the front sight, the shot is a 10 or X.
A strip of tape on the lens works too, especially to just try out the technique.