This picture shows the long range 'side wall' rear sight of the Type I Model 1855 rifle musket used between 1857 and 1858.  By setting the slide on the 'ladder' to rest on the steps of the side walls a notch could be aligned with the front sight for ranges up to 400 yards.  Ranges from 500 to 800 yards could be set by raising the ladder upright (as seen above) and using the notch on the slide itself.  The notch on the very top of the ladder gave a range of 900 yards.

      The simpler leaf sight that went in to service in 1858 had two hinged metal leaves of different lengths that folded down on each other.  The base of the first leaf was sighted for 100 yards, when the first leaf was flipped up the notch aligned with the front sight for 300 yards, and when the second leaf was pulled up the weapon was sighted for 500 yards.

     Because the black powder .58 rifle muskets had a relatively low muzzle velocity (~950'  per second) the ball dropped rapidly upon leaving the bore.  This made estimating the amount of angle for the ballistic arc to hit a target at over 100 yards a difficult exercise and, as neither of the Civil War armies had much powder to burn in target practice, the full potential of the rifle musket was not often realized on the battlefield, where firefights were often conducted at 150 yards or less.