Firearms ownership is deeply entangled with white supremacy; "I can shoot anyone who threatens my social position". This isn't even obvious; this is unmissable.
(Even before you notice that the NRA is an unlawful lobbying organization for the post-state transnational actors pushing white supremacy as a way to get rid of democracy, since democracy actually threatens them.)
Any fix for firearms violence is kinda pointless without a fix for the white supremacy. In an industrial culture, there's an arbitrarily large number of ways to kill a lot of people. Many of them are much easier than the firearms approaches; it's an entirely grim thought, but the focus on shooting people is keeping the casualty count down compared to a political movement trying to maximize the body count by the most expeditious available means. (No matter how doubtful you are of this claim, I am not about to post examples of alternatives. Just trust me on this one.)
Directly opposing firearms gets into a purely tactical, politics-and-morals conflict the white supremacists are well-positioned to win. It doesn't matter that their creed is factually not even wrong; it matters that it's simple and easily copied into other people. Like anything else operating under selection, what matters is how it gets copies into the future. Nuance, accuracy, and facts are generally political disadvantages. They're especially political disadvantages when the other side is specifically opposed. (Because if the white supremacists ever start admitting facts and accuracy they have to look abashed and acknowledge their entire world view is sin in its own terms; cowardice and folly.)
Going for logistics -- quintuple the cost of ammunition; very tightly control gunpowder; move the controlled part (in the US) from the receiver to some pressure-containing part -- doesn't work because the great majority of Anglosphere law enforcement is white supremacist and won't enforce such laws and the white supremacist party has more than enough influence to prevent a distinct enforcement arm from being created at an effective level of funding. (And the legitimate hunting lobby would be opposed, too.)
So what can you do?
Attack weakness.
Attack weakness
in the system, because the fix is a different system.
Especially don't confuse "this is killing a lot of people" with weakness, because to the white supremacist plurality
killing a lot of people is strength. The system proves it works by stacking corpses. Trying to attack this morally serves to prove to the white supremacist that it's working, they should do more of that.
"Shooting sports are awful" isn't weakness; despite recognizing that most shooting sports model accurately as turning money into noise, a great many people sincerely believe shooting sports are fun. (If you can't observe people figuring out they should drive as little as possible and lobby continuously for decarbonization, expecting them to connect up the white supremacy and the shooting sports isn't a practical expectation.)
White supremacy is an ideology of fear; mostly fear of their own incompetence. Fear makes you stupid; one of the consequences of people recognizing that they're (at least relatively) stupid is that they want to forcibly simplify the system around them into a comprehensible ßž thus much simpler — form.
The way you get rid of white supremacy is
not economic prosperity. (That was the Long 50s, up through Civil Rights. It did not reduce white supremacy.) The way you get rid of white supremacy is by doing one of three things.
1. extermination. This is the most expensive option; given that it's
patriarchal white supremacy, don't bet against the consensus of the matrons going for this in a few years as the demographics shift. But as a political plan it's not helpful.
2. systemic opposition. Armed police with a union are a rival power structure to the civil government; they're meant to be a rival power structure to the civil government. (That Civil Rights backlash thing.) Institutional armed force is the monopoly of the state, and so long as there are armed police with unions, this rather essential pillar of civil government is not in place. Whether you disarm the police, make them much more tightly agents of the state (no union; no shred of a union; direct oath, inspections from bits of the bureaucracy outside their influence, etc.), or simply forbid police unions, that's a legislative start. So is assigning terrorist status and applying all the financial penalties to organizations which continue to fund white supremacists. (That is, if someone gets designated a white supremacist terrorist and you can prove they got a paypal donation, paypal gets chapter 7 liquidation after the third one.)
3. Push cultural change. You cannot get "no guns"; you can get "skilled guns" after the European gun club model. (and then it's mostly an old people thing, and boring.) Use it to push firearms out of the home into secure storage facilities where access requires multiple individuals. (Which is what militaries do! The same person doesn't generally have keys to the rifle storage and the ammunition storage.) Make a day at the range require five-actor access; make all ammunition purchases through the gun club. (You can't buy ammo; your gun club can buy ammo for you, it's on the shelf with your name on it, but it never passes into your sole control until you're on the gun club's range.) Require the gun club to pass random inspections, require both approval-of-the-membership, competence demonstrations, and state-administered testing to join; have a small percentage of law enforcement or former law enforcement (like, 10 percent maximum) membership limit; limit total ammunition purchases to whatever is least of four times the amount fired by women members and the amount fired by non-white members last year. (In Canada, Native members would be an interesting third category for this.) (If you can demonstrate falsified records, the officers lose their membership, get fined, and can never own firearms again.) Mail order is fine, but it goes to the gun club under the same five-actor controls. If any member of a gun club participates in a mass shooting, the entirety of that club's firearm holdings are confiscated and destroyed. If you're not a gun club member, you're not qualified to own a firearm. (If you're rural or you hunt, you can have at most five long arms in your free possession, none self-loading.) Point out pistols are useless and dangerous until you can get a home-storage ban. Send high school kids off to "learn safety and scrub filthy bolt components with a toothbrush" summer camps; the mystique of firearms doesn't survive much of this.
I'd be going for a combination of 2 and 3. Note that if you do 3 for serious, there's no reason the club or members of the club can't own a belt fed machine gun if they want to. That will turn a
lot of money into noise, but it will get buy-in into the new system from the mostly-sensible gun owner majority. You want a system where the young and foolish have to struggle for the approval of the old and experienced; you want there to be a graceful way for the not-so-young-now to acknowledge that, yeah, that was a pointless expense, I'm going to get something that lets me work on my group size now. You also sincerely require a social context for all this; that's a good reason to make sure there are urban options, with subsidized (or public) range access as necessary.
But as long as the idea is to solve the
gun problem, nothing will work, because it's a white supremacy problem, not a gun problem. Effective measures must solve the problem actually present.
(Look at all the work done on how prohibition movement was much more about domestic violence against women than alcohol, and how that turned out, and take a lesson.)