Armament quiz, identify the weapon in the picture?

[mindworms]

first one to PROPERLY identify the weapon in the picture below gets best answer. cite your source, if possible.

http://i624.photobucket.com/albums/tt330/mindworms/PICT0004.jpg?t=1252137766
external yes, but not a cannon

 

[AmmoMan]

its an external cannon

 

[bonesaw]

pepperbox