Look at the “training manuals” link at the top of the page. I have added four manuals on making homemade firearms to that page. All of the manuals are in alphabetical order. The new ones all begin with “homemade.”
Since it is easier to make fully automatic firearms than semi, three of them are for submachine guns, and one is a break open. They can all be made with common parts found at a hardware store using inexpensive hand tools.
As a disclaimer, please note that they are being provided for educational purposes only. If you make any of the firearms there, remember to follow the law in making these evil “ghost guns” and you do so at your own risk.