What gun is your "ol' reliable?"

I don't mean "what's your biggest WMD." It doesn't have to be anything that can clear rooms in the pull of a trigger. It doesn't even have to be your most used gun. But when the chips are down, no matter what game mode you're in, no matter what restrictions or resistances are in play, or whenever you're just down for a relaxing time - what's your first gun to go to that you know is reliable?

For me, it's my Corinth Prime. It may not be flashy. It may not be broken. It may be pretty basic, as far as shotguns go.
But she's never let me down.