Volume 20 of Professor Parabellum's Practical Scrap Metal Small Arms.
This volume provides plans and instructions for the construction of a 100% DIY pump-action 12 gauge shotgun. This is the first repeating design for a shotgun from Professor Parabellum.
"The following 12 gauge pump-action shotgun design can be manufactured in the home environment without the use of a lathe or milling machine. The majority of its components are constructed from standard sizes of steel box section and round tubing, including the barrel. 12 gauge being a cartridge which produces relatively low chamber pressures allows the use of a simple bolt locking mechanism, in this instance a spring loaded lug which is keyed in or out of a hole in the thick-walled upper receiver via the rearward or forward motion of the action bar."