Volume 23 of Professor Parabellum's Practical Scrap Metal Small Arms.
This volume provides plans and instructions for the construction of what Professor Parabellum describes as "essentially a weapon on par with an AA-12". These automatic shotguns are fully DIY and can be built without use of a mill or lathe.
Two designs are included in the release package: the OBAS (Open Bolt Auto Shotgun) Mk.I and Mk.II. Plans are included for a 20-round drum magazine as well, although this will be much more difficult to DIY.