I see "J. Ruseborough" marked on the lock plate, not "R. Jonesborough". Am I seeing it wrong, or is it marked somewhere else that does not show in the pictures?
I can't find any info on Ruseborough. Whoever that was may be just the lock maker.
I think the style of the stock, the back action lock, and the peep sight put it in the mid to late 1800's.
Did you make sure it isn't loaded?
Give us some more detailed pictures, especially of any other marks. Maybe some marks under the barrels.