I've heard people use the term "hawk" to describe a sale, but I think you're right. He didn't sell his rifle, he effectively traded it.
I was reading American Rifleman the other day and they had a photo of a bunch of kids holding rifles and that picture was taken in 1929. From then until not too many years ago it was normal to see kids with rifles or shotguns. Real or fake.
Can you imagine the horror if the story about an eight year old trading in his rifle for a washing machine were to happen today?
They'd ban the kid from school forever and have his grandma in jail for one reason or another.
Yeah, but those were the days when we could trust people, because the "gummit" wasn't so involved in lives of families, LOL!
He almost certainly "hocked" the rifle, especially since it went to a pawn shop ("hock" is synonymous with "pawm"). To hawk goods is so sell them in public, typically by calling out; a typical example of a hawker would be the person selling peanuts at a ball game.
Then again, if a computer spell-checker accepts a word, it must be write, rite?