TREVIŅO in the frizzen. This could be either a name of a village or the name of the lockmaker. Given that there is already a place (Coruņa) engraved in the upper part, we must infer that Treviņo is the name of the lock maker, a Galego (Galitian) in/from Coruņa.
I didn't find a barrel (gun) mark with similar lettering in James Lavin's fine work "A History of Firearms". Try to take a better picture; not necessarily larger, but a bit more accurate. We can try and decipher the name that is there, even if it is not from a famous smith.
The
R is a bit rustic; i wouldn't go for "Ripol" or even "Royal". Probably is the owner last name initial, engraved at delivery.
Mind you, i am not a specialist; other members may show up and give you better opinions

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