I made this mod out of love (:P) for Seleziona's break action shotgun, the gun is now a sawed-off shotgun. It is still break action, and the only things that are different include the stock and the barrel extension. The new front barrel part has a little latch that you flip that will allow the gun to break open, you do not have to swing it forward sharply anymore. I prefer using the gray connectors with blue rods as ammunition.
Pretty much the entire thing is part of/was inspired by the design of Seleziona's shotgun. It works just the same, except for the part where you don't have to flick it down, and instead tap the switch. Also, i recommend building the actual shotgun, the link is HERE