El Garro's helpful link references an article speaking to Stanton's three patents (one provisional):
"The first, No. 49 of 8 January 1867, received only provisional protection and used an external spring to lift the hammer to half-cock. Very shortly after this he secured a second patent, No. 367 of 9 February 1867, in which the hammer is returned to half-cock by the mainspring. This he achieved by lengthening one limb of the mainspring the top in a bar-action lock and the bottom in a back-action lock off which the tumbler bounces. And it was this design that was widely adopted, appearing in both new guns and as conversions to existing locks. In his third patent, No. 3774 of 30 December 1869, Stanton reverses the location of the projections on the mainspring limbs for bar-action and back-action locks, adding a characteristic curve to the end of the spring."
I am searching for a photo of patent 3774 to compare with the above photo to see if it is a match. Of course it could have been a conversation, too, as Mr Barclay suggests.
