A 12 Gauge Single-Shot Shotgun design intended to be as simple as possible to build while being as effective as possible.
No 3D-printer needed.
Only a metal file, a power drill and an arc welder are needed.
Partially based on the Single Action Shotgun by Professor Parabellum
NOTE: Currently this is just a reference model and thus you are required to figure the build process out yourself as well as choosing the exact materials and parts.