Aleksrgill,
The first thing to find out is whether something is in the barrel. Might be a load. Or just the ball, which does happen as my friends here will admit. I suggest NOT removing the barrel from the stock. Bring it to a club shoot and let a gunmaker who does this for a living or a hobby assist you with that. Both clubs have gunmakers in their membership.
I would not put a cap on the nipple until I am absolutely sure the barrel is empty. Worst case scenario would be a load of smokeless powder in the barrel (hey, its black, folks would tell me), and the ball. Or a double load of black powder and the ball. Once the barrel is declared clear and safe, then you are on solid ground, so to speak.
I have had customers in their zeal, cracking/breaking the stock's forearm in forcing the barrel out of its channel. So, leave that to experienced hands to perform. Since the initials are on the barrel, chances are they would be the maker's, so no real need to remove the barrel from the stock.
The lock is a "Maslin" design, and looks like a CVA lock. The only other lock maker that had that design was Russ Hamm out of Fort Myers, FL. But lock parts are available for it if its a CVA Spanish lock. I remember also that L & R made Maslin-style locks. However, I think this one is a CVA/Traditions manufacture.
Hope you can make it to either club's match. The Lafayette Long Rifles get-together is about a week from Saturday and gas supplies may be more favorable to make the trip then. Hope this helps.