Good to see all the "do the right thing" replies here.
The question was Hypothetical curiosity based on a real event from my past.
Because this choice was indeed a turning point in my life when it happened 35 years ago at the age of 19. Whether he was honest or not didn't matter. All I could think of was "What if it was my Great Grandfather's Rifle?" and he was indeed being sincere and honest about it.
I did give him the benefit of the doubt and gave it back to him. I would like to believe that this action may have helped towards some of the extremely good fortune I have had in life since. Good to see those who would do the right thing, not just for the guy wanting it back, But for themselves.
Would I do it again today? or tomorrow? Absolutely