When it comes to guns it seems that morals or the lack of them will be tested faster than any other object you can name. I have been through this from just about every side and angle through the years. I have argued over 20 bucks and let good guns get away because of it. Conversly, I have sold guns super cheap where I felt sorry for a almost broke guy. I have flat gave away guns a number of times to people who have done me favors and wasnt looking to be rewarded.
I have had family heirlooms stolen out of my house, and have never got over it. I also have sold some inherited guns when I was young and dumb and have hated and never forgave myself for it.
One time I had a friend/captain supervisor trade me a "blood gun" that the judge gave him when he was a deputy many years ago because he solved the case. I dont know how many times I heard him whine about tradeing me the gun and wished he hadnt. Then one day I located a identical old HDM for sale about 50 years old and unfired. I told frank go buy me that gun and trade it to me for your old one. He wouldnt do it!
I would ask the kid exactly why he wants it as his grandpa never shot it and it couldnt really be sentiment. On the other hand you also havent shot it. From a couple of your other posts I assume you arent hurting financialy, and dont need to sell it.
You know, truth is, if your something like me, we have classic guns in the safe that never get shot, are "queens". Someday we croak, the guns probley get sold eventualy dirt cheep to someone that also puts them in the safe to never be used to. When we were young certain guns appealed to us and got shot a lot. In my case I bought my first good revolver, a single six when I was about 19. I shot that more than my last 50 exspendsive safe queen revolvers put together!
This may be a big deal to the kid even if his reasoning isnt like yours. You probley could give it to him for free and it probley wouldnt change a minute of your life. I once had a springfield 45-70 carbine for sale at a gunshow back in the 1970s. I forget what I had on it. Some nice young guy pulled out every dime and bill out of his pockets and was something like $40s short back then. He was literaly almost bawling! In a weak moment I handed him the rifle and scooped up the money. Giveing up $40s didnt change my life. Wonder if he remembers it like I do.