Problem is that it's too late for that to happen. There's too many guns already in circulation and a stronger gun culture in the USA.
Japan's gun ban in the 1970's was effective primarily because there were so few guns in civilian hands even before the ban. Same goes for a lot of the restrictions in European countries.
Manchin will probably be the one thing that keeps gun control from going through since he knows he'll both lose his seat and the Dems will lose their majority if he does vote for it.
Pretty much this. Manchin is to the Democrats what Roberts and Romney are to the Republicans and with Manchin, he's going to be a lot more likely to vote red both to keep his own seat and to keep the razor-thin majority the Democrats have in the Senate.
If just one Democrat senator loses in the midterms, the GOP gains majority control of the House in 2022.
And before you invoke "muh voting fraud", I highly doubt the DNC's political machines are strong in West Virginia, at least not anymore.