I honestly think that anything short of straight up banning the sale of gunpowder will have a temporary at best effect on gun violence, and do less than nothing at worst.

I don't even think that would really help all that much. You would maybe increase the relative complexity required to build a gun, but I think you'd still get plenty of people who are able to utilize improvised home explosives in their homemade firearms designs. Of another variety, you'd also probably see a rapid influx and growth of the airgun market, which is already pretty far along in it's ability to substitute and even outclass normal firearms, in some respects (mostly in cost, and consistent shot over shot accuracy, rather than in "combat efficacy", depending on what you mean by that). I'm also sure you'd see designs that adapt more mundane forms of explosives. Propane strikes me as a particularly good candidate, but you could also probably just use normal gasoline as a propellant, hydrogen peroxide, H2O2, butane, you could probably even use wood gas.

I think there are too many machine shops in america to realistically stop america's position globally as a firearms manufacturer, in a vacuum. As you say, you'd need to more combat the external factors going into it, rather than trying to kind of, try to make sweeping bans around it. Especially as those sweeping bans can be more selectively applied to particular communities, to increase their criminalization, as we've seen time after time.

The caveat I would place around that, is that handguns are a pretty terrible suicide vector, I think it's something like half of all gun deaths are suicides. Of suicides generally, about a third will never try again, and it's a spur of the moment decision, and about a third will repetitively try over and over, with the remainder falling somewhere in the middle of multiple attempts. So preventing guns from falling into those, at least third, of hands, could be a good form of regulation. Though, that point is somewhat unrelated to the conversation at hand, here, I just think it's a pretty good point I don't hear people bring up a lot.