If the goal is "no mass shootings in the US", then no, there are no solutions outside of "no guns". And that's no solution:
"Make sure that the Democrats have a supermajority in both Houses and the Presidency, as some Democrats hail from strong 2A states and you may not be able to count on their support. Have your legislator introduce legislation amending the Second Amendment, and getting everyone to decide on the terms of the new Amendment. Get 2/3 of both Houses to agree on the wording and vote to amend the Constitution. Make sure that Amendments 4 and 10 don’t get in the way of your new wording. Now get 38 state legislatures to vote to accept the new Amendment. Don’t count of the votes of Vermont, New Hampshire, North Dakota, South Dakota, Montana, Idaho, Wyoming New Mexico, Arizona, Oklahoma, Texas, Mississippi, Alabama, Tennessee, Georgia, Florida, South Carolina, North Carolina, Arkansas, Missouri, Kentucky or Kansas. That leaves you about ten states short, but hey, voter fraud happens, so you might be able to pull it off.
Now what? The laws currently in place are still in place, regardless of the status of the 2A, so effort has to be made to change them. Given that 12 states voted against the Amendment, they aren’t likely to change their laws, and you can’t count on all of the other states imposing the same draconian laws that CA and NY are likely to impose. There are still 325 million guns in private hands. There are likely 5-8 million “patrol rifles’ in private hands, along with say 20-50 million 30 round magazines. There are billions of rounds of ammo in private hands.
Now try to find and collect all of those guns. Try getting funding to pay for $325 billion in buy-backs for the guns, and another $100 billion or so for the ammunition. Try to convince the people that you want going to get the guns that they need to give up their privately owned guns, too. Try getting people to register their guns so that you know where to get them. Ask Connecticut, Canada and Germany how well their gun registration efforts worked.
Next, prohibit, find and confiscate any bit of machinery that can be used to manufacture firearms, like CNC machines, milling machines and 3D printers.
Lastly, try closing the porous 1000 mile border between the US and our lawless neighbor to the south. "