The black market isn't a magic place immune to the laws of economics. Before the smugglers got involved, beer was expensive and there wasn't enough of it - so people started drinking weird shit brewed in someone's bathtub. If marijuana is cheap in your neighborhood, there's probably someone nearby growing it in their kitchen - good quality marijuana with high concentrations of THC is too expensive for most casual users to afford.
You CAN'T make guns in your bedroom. You CAN'T make them in a bathtub. You can't even make them in a garage. They require such specialized machining that we can - and do - count and keep track of the number of facilities that even have that capability. People got excited about 3D printed guns for a while but those turned out to be crap guns - I'm not scared of a mugger who has a shit gun that if he shot me with it, I'd go "ow! That's REALLY annoying. Stop that."
So by any analysis, black market sales of guns are HEAVILY affected by the supply bottlenecks, which can be restricted by legislation. And guess what, your weak assed myths about guns are losing their power over people, because your arguments were a house of cards from the start.