Exactly, Anandalal,
It's a notable find anyway!
The Inca culture died about 500 years ago, almost 100 years before that gun was manufactured. No trade relations between the Iberian Peninsula and the Southern American continent have ever come to my knowledge though. What's possible: that the stock ornamentation is 19th c. Historismus fantasy. I'm afraid though no final judgement is possible without close scientific inspection - and I am certainly not expert enough to do that.
Best,
Michael