Thomas Simpson is believed to have made the famous Casper Mansker (1791) rifle and is associated with the same group of gunsmiths as Jacob Young. There is a lot of ongoing research regarding where all, and when, he worked. Your rifle, if made by him, could be a very important piece and I would love to see photos. The Mansker rifle has one of the finest examples of the captured lid style patchbox known to exist. There are others on here who know more about him than I do - hopefully one of them will add to this post.
(Also sent you a personal message via this board).
Guy
