User blog comment:Warmachine375/Gun-Gun Weapons possibility?/@comment-73.136.18.37-20150530152820/@comment-25396609-20150530201137

when switching from rifle to shotgun, the box magazine and receptacle disconnect and slide into a slot in the stock, then a tube magazine situated under the barrel slides back and connects to the loading mechanism, while the bolt disengages and the firing mechanism connects to a pump action on the tube magazine.

not that difficult.