"The heavy barreled long-range muzzleloading target rifle shown above is of the typical 1840's thru 1860's design, and so is the early telescopic rifle sight that's mounted on this rifle. This was the 'high performance muzzleloader' of its day, and when shot by an accuracy conscious shooter who took the time to find just the right combination of powder... charge... bullet... and whatever else it took to get the absolute best accuracy from the muzzleloader, and who precisely built each and every load exactly the same, these rifles regularly produced 10-shot 200-yard-plus groups that were less than 2-inches across center-to-center.
This particular rifle, and telescopic rifle sight, was built by master riflesmith Morgan James, of Utica, NY in probably the late 1850's or early 1860's - and saw service during the Civil War as one of the very first telescopic sight (a.k.a. riflescope) mounted military sniper rifles, or as they were known then, a Sharpshooter rifle. Typical of the period, this rifle was likely of .40, .44 or .45 caliber, although .48 and .50 caliber was fairly common as well, and rifled with a fast turn-in-18 to 22 inches rifling twist. The bullets that performed so well out of these rifles were generally three or more times in length as in diameter, and needed the fast rate of rifling twist to stabilize the lengthy projectiles in flight - especially when shooting at 40 rods (220 yards). The big lead bullets commonly weighed, depending on the caliber of the rifle and the rate of rifling twist, between 400 and 600 grains, and were often paper patched for best long-range accuracy." - NORTH AMERICAN MUZZLELOADER HUNTING
Beginning in the 1830's, long range muzzleloader shooting took a giant leap forward with the earliest development of elongated conical bullets - which could retain velocity far better than the old patched round ball projectiles dating from basically the very first muzzle-loaded firearms several centuries earlier. With the refinement of those bullets about 1835 to 1840, accuracy minded shooters began to learn that the rifles then being specifically built to shoot conical bullets were capable of shooting with greater accuracy than the human eye and open sights would allow them to shoot. That's when a few ingenious rifle makers began playing around with the development of the first "telescopic rifle sights"... which we now refer to as riflescopes.