A flintlock pistol ... with a Portuguese lock.

[Dmitry]

Originally Posted by fernando

Regulation means what it says: regulation.

Thank you. I did not know that.

If this was a regulation piece, it should be easy to research. Lack of decoration on the stock suggests that it could've been an issue weapon, in which case you should see similar examples.
The lack or a band securing the barrel to the fore-end of the stock is also unusual, but I don't know anything about Portuguese firearms...