I'm relying on my memory here-so don't take what I'm going to say as the truth, but I seem to remember that early telescopic-like sights were nothing more than a hollow tube with cross hairs in them. What gave them an advantage is the bases that attached the tube to the rifle were adjustable elevation, and perhaps windage too. But other than the cross hairs, the tube was hollow. Perhaps that's what Malcolm did to create what we would consider a scope, he added glass magnification?
To take this thread down a slightly different path, the following system was state-of-the-art, although in the 1870's-1880's, for long range shooters. I have a reproduction 1874 Sharps rifle and have these types of sights on them and can confirm they are very accurate. Think of the "bucket" scene from the movie "Quigley Down Under," and you'll know what I'm talking about
This is the front sight, which would mount to the barrel via a dove-tail cut. It has a bubble level in it to prevent the shooter from canting the rifle (doing so would throw the round to the right or left). The cross hairs can be changed via an insert that slips into a slot in the top of the tube sight. Some of these sights had a screw in the base which would allow the sight to move in either direction for windage adjustments.
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This is the rear sight, called a Vernier Tang Sight, and would be mounted to the tang of the barrel. You look through the little hole in the middle of the round eye piece, and on some sights the aperture was adjustable to let more light in which would help to(0 throu sharpen the front sight image. The round wheel at the top of the sight is the adjustment for elevation. On the base there would be another screw piece that would allow the sight to move either left or right for windage. On the side of the sight staff you'll notice a set of marks that run for most of the length of the sight with the numbers 1 and 1/2 on it. There are 20 marks to the inch. Just to the left of these marks and a small slider with 6 marks on them, (actually the bottom mark is 0, then 5 more marks higher). This slider is what is moved up or down to change elevation and the combination of the 6 marks on the slider and the 20 marks on the staff gives a possible elevation change point to point of 1/100th of an inch. In the hands of someone who knows their rifle and how to use these type of sights, long range accuracy can be outstanding, and there is no magnification involved. You just need good eyesight. In 1874 at the Second Battle of Adobe Wells, Billie Dixon, a buffalo hunter, using a borrowed 50-90 Sharps rifle, killed an Indian warrior at 1538 yards, or 7/8th of a mile.
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