I'm a little concerned even if it may be irrational. But he's pretty antisocial, doesn't have any close people in his life (I tried to be but didn't work out, he also doesn't believe people can be close emotionally), and is very low in empathy. He can be a bit aggressive at times too. I'm not sure if I'd say I've ever seen extremely concerning behavior from him, but this move of buying a gun does concern me a bit.

I spent 2 years trying to get to know him and support him and become close but it never went anywhere. He has no interest in other people and even said so himself that he doesn't care. Which is weird given that he reads self-improvement books, some of them even being on socializing

TLDR: Nephew bought a gun, worried because of his behavior traits.