You would think that people interested in such an historic hobby as black powder shooting would go to the trouble to learn some of the history. A strange idea in today's world, of course.
Charles Wilson Peale, the preeminent portrait painter of the Revolutionary period, put a telescopic sight on a flintlock in 1775. His notes about it are at this link.
allthingsliberty.com/2013/07/charles-willson-peales-riffle-with-a-tellescope-to-it/
In 1808, Henry Beaufroy described the use of telescopic sights on flintlock rifles in England.
_Scloppetaria: or Considerations on the nature and use of rifled barrel guns, with reference to their forming the basis of a permanent system of national defence, agreeable to the genius of the country_, by Capt. Henry Beaufroy, 1808 [Henry Benjamin Hanbury Beaufroy] Originally published as _Scloppetaria, by a Corporal of Riflemen_.
“Others again have had a small telescope instead of an after-sight: the accuracy with which shooting may be conducted by this manner, is amazing; for although it required much trouble to arrange the apparatus for any particular distance, yet once done, the bullets would cut repeatedly one into the other, and not infrequently a second shot would so completely pass through a former, as scarcely to leave any additional indentation on the edge. Their liability to be out of order, however, has precluded their frequent introduction; the sight being adjusted by means of two cross wires in the tube of the telescope, similar to those used for transit instruments, the very jar of the piece firing will very soon alter their position, and consequently their accuracy can no longer be depended upon.”
Spence
