The thing people do not understand is that firearms are (mostly) steel. It takes about $2400 worth of equipment to set-up a system that would allow you to manufacture firearms (not necessarily high quality one, but workable ones). If I am going to manufacture illegal firearms, it is simpler to make fully-automatic ones than it is to manufacture semi-automatic ones -- look at the history of firearms and you will see that fully automatic firearms were developed more than two decades prior to semi-automatic ones (though I will admit that a highly reliable, reasonably accurate, fully-automatic firearm is much more of a technical challenge than highly reliable, reasonably accurate, semi-automatic firearms are to make). Notebooks from people such as Garrand and Turpin are "findable" on the internet.
Modern cordite & BKNO3 propellants and azide-based primers are items that, were you to attempt to make them at home, you would be caught -- by your local fire department! This is why commercial propellant and primer lines are design to limit the damage when they catch fire in production (having designed my fair share of such systems over the years).