Supreme court shot down the 20k for pell grant recipients and 10k for non pell grant recipients plan, and basically said that at that scale should require congress. So all the smaller programs have been calibrated to try to survive the court battles.
A tariff on steel and aluminum will have much farther reaching consequences than guns. A specific tariff on smokeless powder is pretty unlikely, though maybe could be part of trying to ramp up domestic production. The US military is trying to make that happen, but that’s kind of the opposite of what you want.
I don’t know that biden truly had the ability to stack the court, any justice he wanted to add would have to get through the senate. Which was only very narrowly held by the dems, and a pretty minimal amount of defections would have scuttled the plan entirely while also having broken the taboo. I don’t actually trust biden either, so the world in which biden destroys the democratic norms and seizes power in that way also is a really bad situation.