]A perfect type of cylinder is used in Calico guns
http://world.guns.ru/smg/smg57-e.htm, which was later placed under the barrel in Bizon SMG
http://world.guns.ru/smg/smg08-e.htm, so I don't think it's useful to invent something new. I'm sorry to say that, but (OMG!) 6 tubes, and only 4 rounds in a tube. To my mind, it's just a waste of space. Moreover, can you place much under the barrel? If it is strongly preferable to use a bolt-action rifle, it would be easier just to use the magazine feeding, as in the original. Or I completely miss the point?