In the Dark Knight Rises Batman tells Catwoman: "No Guns!"

[Prophet 451]

20. Batman has been very anti-gun since the early Forties

He used a gun in the first few stories but it was pretty quickly decided that he wouldn't and those stories were retconned out of existence. Since then, Batman has been portrayed as very anti-gun (to the extent where it's been a plot point several times) and absolutely does not kill. He has carried and used a gun exactly once in modern continuity (against the god of evil, Darkseid in the very confusing Final Crisis event). Now, most superheroes avoid killing when they can but Bats is pathological about it. He refused to even kill the Alien-infected captives in Batman Vs. Alien. Even Superman tried to kill Doomsday but with Batman, it's never even a question.

Yes, I am a complete geek.