I remmember going hunting with my grandfather. He had an old 45-70 gov. single shot open sites. I was very young then. When a deer or elk was spotted he would hold up his finger(still dont know why he did that). he would sit down and load it,raise and adjust the manual range finder on the front site. and shoot, sometimes missed but mostly he would hit it. now that Im older I wish I would have asked him how he knew how to range the animal.