+1. RCA #42, the Leyendecker box and the Deschler rifle could all be within 5 years of each other. The Leyendeker box is dated 1771 IIRC and may or may not be the latest of the 3. Of course although in "evolution", the found examples are not necessarily the very first ones ever made. Seems the Christians Spring cast side openers (entirely different construction) co-evolved or were slightly later than RCA #42 by many estimates.
Disclaimer:No real data was harmed in my regurgitation of research done by others, to whom I owe a debt of gratitude.