Up until the point where telescopic sights (scopes) became reliable enough, metalic sights were the standard. Among metalic sights, the aperture or peep sights provided the best accuracy. The Lyman company first started manufacturing aperture sights in the 1880's. For lever action rifles, they were typically mounted to the stock behind the action. After WWI, bolt action rifles started being used widely for hunting and for these rifles, peep sights were mounted on the receiver itself. There are a number of advantages to a peep sight. Since they are mounted so far from the front sight, they are inherently more accurate -- this is a matter of geometry.
Consider a line with points marked A, B and C where the distance AC is twice the distance AB. Now mark points B' and C' by measuring distance x perpendicular to line AC at points B and C. Now, if the angle C'AC is θ, the angle B'AB is twice as much, it is 2θ. An equal displacement at the greater distance has a smaller effect allowing for finer sight control.
The other advantage of the peep sight over open metallic sights is that the human eye naturally centers the front sight in the center of the circular opening of the aperture. This makes for quickness and accuracy in the aiming process. The physiological effect is so strikingly effective that Elmer Keith recommended unscrewing and discarding the small target aperture as soon as the sight is mounted. The open hole the target aperture screws into is larger and so quicker to sight with.
I have a Lyman 48 peep on my elk rifle. If the snow is blowing I can remove the scope and attach the peep slide or, to use the scope, I can remove the peep and attach the scope. The drawback is that when the scope is attached, the open slide is ugly and it leaves the small indicator liable to damage.
To resolve this issue, I decided to make a dummy slide to fill the gap when the peep is not installed. I filed some mild steel into the required dovetail shape.
After sanding it smooth and cutting it to length and I blued it using Brownell's Oxpho-Blue cold bluing liquid.
The finished slide fits snugly and gives the rifle a finished look when the scope is mounted.
The scope mount is a Griffin & Howe side mount which allows the scope to be easily removed and when remounted, it goes back to zero.