Some more information would be helpful; how long is the barrel ? and the other questions posted by
@Ralph Heinz.
The "S&S" stamped inside the lock would be the lock maker, in this case W. Scott & C. Scott, important Birmingham gunsmiths. The other initials are the lock inspector, there were many, and it is if no significance to further ID's.
The stock has been heavily sanded and I'd think most of the marks are long gone.