Hold up a minute, folks-
Alard, I show an internet provider for you that is outside the US. I mention this for a reason- to explain the folks that may respond in a "less than friendly" manner.
In the US, it is HIGHLY illegal to build a fully automatic weapon without having a special license. To do so carries a penalty of 10 years in prison, and a fine of up to $250,000- along with loss of your rights to own ANY firearm.
It is no uncommon for us to run into a new person that is not fully aware of the laws they are under here in the US- and are about to do something really- I mean REALLY stupid. The folks here are not shy about telling them that they are stupid.
However, IF you are not in the US, and under US law, that does not apply.
A pistol caliber sub-machinegun is actually one of the simpler firearms to manufacture. During WW 2 the British designed and built the STEN, known as the Plumber's Nightmare- it looked as if it were made of sections of pipe. The difficulties will be finding the correct grade of steel, rifling of the barrel, and the correct weight of springs. Skills in the use of machine tools is also helpful, but generations of Afghan gun makers have shown it is not essential, only helpful.
What we have here is... failure- to communicate.