Hi,
Those are post 1813 Birmingham proof marks on the barrel. The T. Ketland & Co. lock was originally flint and dates probably to the early 1800s. The brass mounts look to be from an inexpensive English export gun. I suspect the gun was restocked from older parts. The percussion conversion is rather poor because the hammer does not strike the nipple squarely. The hammer may be a later ill fitting replacement.
dave