"In 1855, Wm. Malcolm opened the world's first true riflescope manufacturing company in Syracuse, NY. Several things set his scopes apart from all of the custom built scopes that had been produced prior to that time. Malcolm's scopes were the first to utilize a 3/4-inch diameter seamless steel tube, and lenses set into brass cells or mountings that were held in place by screws, which were not affected by recoil. More importantly, the Wm. Malcolm scopes, which were offered in magnification ranging from 3x to 20x, featured an adjustable ocular (rear) lens. This scope could be quickly and easily focused to the individual shooter's eyesight, meaning these scopes could be sold by any general mercantile store or gunshop. Likewise, since the scope required no custom lens grounding, the cost of the scope was considerably lower. Malcolm also made the mounts for his scopes more easily adjusted than earlier rifle maker produced telescopic rifle sights - and the parts were interchangeable." - North American Muzzleloader Hunting

This is an excerpt from and article/report just published on the NORTH AMERICAN MUZZLELOADER HUNTING website that takes a good look at how the long-range accuracy of the muzzle-loaded bullet rifles produced through the 1840's into the 1860's led to the development of the earliest riflescopes.  Here's a look at the key people who worked to tap the accuracy and performance of the rifles built during that period. For the full article, go to the North American Muzzleloader Hunting blog.