Homemade firearms are quite easy to make. The only reason we don't see more of them is because people still have access to factory firearms. If the government somehow shuts that down, countless people will simply start making guns at home and selling them.
Gun laws are useless for criminals who are willing to kill. All gun restrictions can do is force law-abiding citizens to disarm themselves.
Sounds like a good way to get seriously hurt. There is no way that a plastic bolt on a plastic receiver would be anywhere near strong enough to safely fire anything more powerful than a .22 lr.