Pill locks were used quite late in New York. Author Edward Barber, in "The Crack Shot or Young Rifleman’s Complete Guide" published in 1868, wrote “Seth Green, the best shot in New Your State, and an ardent sportsman, prefers a rifle made by Billinghurst, of Rochester, on Miller’s [sic] patent.” He goes on to describe the pill lock revolving rifle, and notes the priming pills in their recesses are covered by tallow to hold them in place. (Page 251-252)
Samuel Morrison, gunsmith in Milton, PA (Upper Susquehanna) got a patent in 1836 for a unique lock with (among other features) an interchangeable system for percussion caps and pills for ignition. So the cap won out, but pills had a long run of use.
Additionally, EC121’s suggestion makes sense, too. In the 1950’s we couldn’t find percussion caps where I lived and I used strike-anywhere kitchen matchhead tips and tape for percussion primers. Maybe removing the hammer insert again and measuring its thread diameter and pitch, and then comparing that with modern standards might help settle the issue.
Bill Paton