OK probably should have expanded. I don't think it would have originated from slang, ops brevity codewords follow a pattern so they are easy to remember. Codewords that are used to described launching and ordnance states are commonly gun related or gun types: e.g: shotgun, rifle, magnum, sniper, shooter. I reckon that Winchester is just another name dreamed up by the doctrine nerds that fits the ordnance theme (because its a common ammunition type).