The only sure way to get the right gun is the Netflix method.
Go to Netflix, click Genre's, scroll to Action & Adventure, select the movie in the list that is the same as your brother's birth month, view movie, buy first gun you see kill a bad guy.
This is fool proof, you will buy a gun, maybe not the right one, but at least he'll have one. One is a start, then he can pay more attention and get one that fits his hand, shooting style, caliber preference, etc.
Join the NRA! Stop the Brady madness!