Oh dear gawd
Why not spend some money buying a decent sized 2nd CNC maching center?
$5K should get you something decent if not $10K
You can get the gun blueprints and make every part quite easily* and the only time you have to check with the boring old regulations is when machining aforesaid lower reciever.
Of course after once making a little popgun, you'll get the taste for making proper guns such as semi-auto 50 cal rifles, or a copy of the famous MG-42 machine gun**
Since footnotes are the way of things today
*easily means being able to program the mill and have enough skill/knowledge to set the thign up and machine the parts correctly... about 5-7 years is ideal
** ammunition costs usually make MG-42 ownership very expensive.. especially after the first 1000 rounds
*** 30 yrs experience of wrestling CNCs and robots to do his evil bidding to make everything from nuclear reactor gas seals to various aerospace stuff and a long history of making high quality rifle parts