The "when did back action locks appear" question has been frequently discussed. In prior discussions with Jerry Noble of southern longrifle fame, he thought they they had been around from back in the mid-flintlock era on swivel breech rifles. They were here before and after the conversion to percussion locks, used at first on swivels, perhaps on other "specialty" guns, then they became more acceptable on single barrel rifles. Their growing acceptance was supposedly based on the realization that it was a superior lock design over the front action lock and did not weaken the wrist area quite as much as a front action.
I have an original Bardstown, KY, rifle (superior quality) with a back action lock; the barrel has an original date of 1837 with the signature, and the lock was a commercial product purchased from the large Moses Dickson shop in Louisville, KY. Only thing it really proves is that back action locks were commercially available to gunmiths in Louisvllle, KY, by 1837. Louisville, with all its river traffic, was perhaps the most commercially progressive town in Kentucky at that time due to all the eastern "innovations" coming in by river boat on a daily basis. The Bardstown rifle mentioned above has a "sister" rifle that is virtually identical, but perhaps a year earlier based on butt architecture and incised details, and it also has a back action lock. Shelby Gallien