John, I did not add the lower picture, Mike, skeettx did. He showed it just for comparison.

All Syracuse hammerless and all Fulton hammerless up until 1907 were on a Regular frame.
The comparison still shows what the lock formation was when the change did occur. An 1888 catalog refers to just having one spring, a mainspring and dispensing of a sear spring.
This feature took place earlier and a guess would be sometime in early 1887.

David