Why was he searching for quiet rifles, didn't he say he can't buy a gun legally? That knowledge is useless without the knowledge to also illegally get a gun and, unless you have connections...beggars can't be choosers. You'll take the Hi-Point and you'll like it. I'd imagine, at least.

Or maybe he wasn't officially barred, he was just so neurotic he wasn't going to lie about his suicidality to the military, or something.

I guess he's nutty, it doesn't have to make perfect sense. Despite him being a "very logical person," in his words.