I discovered in fooling around with the Marlin 989 M2 I bought the other day something I would not have believed had I not tried it. The rear sight on this little critter is a clamp-on gizmo that fits on the dovetailed receiver. Being an old f--t with astigmatism AND presbyoptia my eyes just don't see open sights very well any more. However, I noticed that when I slide the rear sight all the way back to the rear of the receiver dovetail, the open notch blurs and shows lots of light around the front sight, just as an aperture sight does. My eye then automatically centers the front blade. It seems crazy to have an open notch rear sight that close to your eye, but it works. I can hit acorns and thumbnail-sized chert rocks on my backstop with this rifle. Haven't been able to shoot that well with open iron sights in years.