Ou don't need much of a rear sight on a fowler. I recommend a low-- very LOW-- open rear sight, with a very wide notch, and minimum height on the "ears". A scratch line in the middle of the bottom of the notch at the backside, is all your eye will need to quickly " Center " the front bead in the notch to eliminate windage, and canting problems. If your fowler has a blade front sight, instead of a bead, the center reference will work, too. You can mark the back of the front sight to shoot round balls at various distances, using bars to tell you how much of the sight to hold UP in the notch for the longer distances.