> What he built was more of a hand cannon, because it’s very difficult to make proper cartridge style ammo without factory made precursor components.
For now, yes. A year or two from now? I would be entirely unsurprised to see CAD files to 3D print casings designed to be loaded with homemade black powder / arbitrary projectiles and ignited via some external source (e.g. an automotive spark plug).
Even ignoring that possibility, the fact that some guy with a homemade electrically-ignited handcannon killed the leader of a country with some of the strictest gun control laws is itself a nail in gun control's coffin.