Here is a neat little design for a very simple homemade M11 clone sent in. It is assembled mostly from pieces of steel box tube and bar stock telescoped together.
The prototype shown was built as a non-firing display model with a dummy bolt and barrel for legal reasons, though it perfectly demonstrates how a compact commercial design can be constructed with little more than a drill, angle grinder and welder.
…. and part 2
Note: These schematics are for academic / technical study purposes only.