Hi. I am a long time reader of this forum, but I haven't posted much. I need some help. I have a Remington 870 with a rifle sight Hastings slug barrel. I have been having trouble adjusting the sights. I was sighting in at 50 yards. I have the left and right part adjusted right, but I can't get it to hit on vertically. Right now it hits about 4 inches above where I aim. From what I understand, that means I should turn the adjustment screw towards "Down". The problem is, it doesn't go any further in that direction.

So, what can I do? Am I even turning the screw the right way?