What is the BORE and what is the LENGTH OF BARREL?
I have a very similar-appearing gun, came from Newfoundland, described as a Three-Quarter Gun. The 46-inch barrel is a .751, making it about 11-bore.
Many of these were made as 'prentice guns by the apprentices at the big London and Birmingham gunmaking shops. Apprentices worked on these cheap ($6 to $9) guns until they were good enough to go on to making fine doubles. Army-type Locks were used on MANY of them because it was a good, proven design AND most of the shops were set up to make it because of Army procurement policies up to the point that Enfield could handle all the needs. One thing you will find is that even though many of these 'prentice locks will FIT an Army rifle, often they are of inferior quality, sometimes even with unhardened Lock-plates.
Apart from rust, one problem common to many of these is the Hammer recessing itself over time from battering against that Nipple, which WAS hardened. I bought a small welder last year in order to repair my own Three-Quarter Gun, which has this problem.
I do know that so many of these were made that Ashbourne's in Twillingate still was advertising them as late as 1902.
There is nothing wrong with the Barrels on these; they took exactly the same Proof tests as the expensive ones. These just were a bit heavier.
These are a fun old thing and, even if you are not out trying for a "shot of ducks" or a mess of Turrs, you can still patch up a .69" or .72" Ball, put 70 grains of FFg behind it and amaze yourself with what it will do to a railroad tie.
Wonderful old piece!
Do have fun!