Indeed they are. Back in the '70s I had the opportunity to examine a demilled Sten parts kit at a gun show. All the parts could be made with simple tools and patience. The most difficult part would be to rifle the barrel if you did not want a smoothebore.
However, even that can be accomplished using electrochemical etching techniques.
If you ever get a chance, take a look at an M-3, “Grease Gum”, .45 cal full auto, 2 moving parts and a couple of springs. Nifty.