stupid ass question but how exactly did he get ammo? like it's not the easiest thing to make yourself. you gotta get a primer, smokeless powder, all that shit.
Not really? You need metal of some kind and black powder. That's trivial to get.
From what we've seen, this was basically two shrapnel pipe bombs strapped to a 2x4 with an electric igniter and one side open to direct the blast. I think just about any one of us given 5 minutes on google or youtube could have made this "gun." In fact, without any knowledge, lets see:
There's your gunpowder.
Ammo... first thing that comes to mind, since I use them for weighing down Warhammer 40k bases and they're on my desk -- Sinker for fishing. オモリ. There's your "ammo." (Use bolt cutters to chop them up into smaller pieces, I guess?)
Battery from an RC car or similar, just needs to arc across a small air gap wire circuit. Grip from any number of plastic toys to complete that circuit. 2x4 and pipes + pipe ends from any hardware store or construction site (they're ubiquitous in Japan). You could use nuts/bolts/nails/etc from the same hardware store, too. Some electrical (or duct) tape to hole it all together. (My theory on the 3x3 one with an iPhone, if that is a phone, is that he was hoping to set up a turret or remote controlled version, but that's just spitballing.)
This will, I won't say get memory holed, but I doubt this will help the Gun Grabber agenda. This guy made something literally any reasonably handy person could make. Note that 5 minutes ago I wouldn't have known how to make this, I literally just took what we've seen and did a few minutes of research, and I'm a glorified computer janitor. And yes, 100% ABSOLUTELY got myself on a government watchlist by searching "how to make black powder" and the like, I'm sure.
No amount of gun control could have stopped this. Somewhere, the elites of the world are sleeping a little less sound tonight.