The act of masturbating. Just another name. When you have shot your gun, you have masturbated. One can use cod perks to further describe their experience, like steady aim, extreme conditioning, or assassin.
-"Yo bro, where were you last night, I didn't see you at the party. Were you shooting your gun??"
-"Yo sorry man I was shooting my gun using extreme conditioning last night to pictures of Kate Upton."
-"Oh don't worry about it man, everyone does it."