I think your problem is that you are turning, following your oponent's moves and thus, even though your gunsight may be "painted" on target, your rounds don't land. You need to remember that if you fire while turning, the rounds will be well below the nose of your plane by the time they get to the target, so if he is in your site, you are actually firing behind him. To land rounds on a maneuvering target while you are maneuvering, you must turn inside the oponent, to the point you cant even see him because the nose of your plane obstructs your view and fire, the hit sprites usually show up even though you are looking thru your plane. The problem is, if he reverses while you are in this position, you won't see him do it and you'll lose him.
Try getting him in this position, fire a quick burst and then flatten your turn to make sure hes still there, If he's not reverse.