A .38 Special Single Shot Pistol.
Can be made with basic hand tools, a 3D-printer and an arc welder.
Uses metric raw materials and off the shelf components,
Partially based on the "Homebuilt 38 Special Pistol" by Gary Coldiron
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.