The dirty little secret that nobody talks about is that making a decent home-made semi-auto is considerably harder than making a decent home-made full-auto.
The semi-auto needs a separate firing pin, a disconnector, and generally a fairly complicated trigger system.
A full-auto just needs a bolt with a nubbin on it to act as the firing pin and a trigger that catches and holds the bolt open unless it's pulled.
What it boils down to is that if there is sufficient demand for multi-shot firearms to generate an illegal market in home-made guns, it makes sense that full-autos would be more common products than semi-autos.
<<<Or just read Nickel-Plated's post directly above mine.
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