Well the biggest concern I have is if you do it, you cannot tell us, why? You're become a criminal producing a firearm illegally and a prohibited class firearms. Even if it's only semi auto you're still in a hell of a trouble. Best thing you can hope for is that the Japanese Official did the test already and it didn't work. Second thing, even if it did work and you didn't get caught, you're risking you're phyisical life as the pressure of a bullet "might" potentially shatter the lower receiver.