A simple approach to make the gun industry responsible would be to make it THEIR problem.
For every death caused by a gun, fine the manufacturer $5 milliom -- instantly, with no excuses and no exceptions. Require them to keep a reserve fund that the government can instantly tap for this very purpose. Also require them to purchase insurance with unlimited liablity coverage if the reserve fund is insufficient. (I.e., worst case the insurer loses everything.) Provide for lengthy prison sentences of all officers and board members if they fall short in this obligation.
Then after each death, once the gun manufacturer has paid their fine they can pursue civil litigation at their own expense to recover their loss from the retailers they sold those guns to. The retailers who are forced to pay up could then sue the owners they sold the guns to, collecting whatver they might. If that owner sold the gun to someone, they are free to find them and sue them.
This would motivate the gun industry itself, using their considerable wealth, to pursue most of the other suggested remedies that are out there:
Under that simple law, the gun manufacturers could continue to do business as usual, probably raising their prices quite a bit to cover this new expense.
Or they could stop making high-capacity weapons, to reduce their liablity.
Or they could design weapons that are impossible to retrofit to be fully (or perhaps even semi-) automatic.
They also might be reluctant to do mail-order sales of 1,000 weapons to John Smith in Gun City, Virginia.
And if the retailers were also on the hook, they might have an incentive to insist that potential buyers (a) were not violent felons, (b) were not living in the same building as violent felons, (c) were sane, (d) were not going through a divorce, (e) were not the subject of restraining orders, (f) owned a gun safe, (g) didn't live in a bunker and alredy own 83 guns and 30,000 rounds of ammo, (h) had sufficient liability to reimburse the retailer if their guns were used to kill 26 people. For starters. I'm sure their lawyers would fill out the check list.
Walmart has deep pockets, but even they might take notice of billions of dollars of losses each year.
Who knows, the purveyors of guns might even lobby the federal government for a national registry so they could know who to sue to get their money back when such guns were used to kill people.
This isn't rocket science. Right now they take the profits and force society to absorb the costs. As long as that single fact remains true, NOTHING ELSE WILL MATTER -- guns will contine to be distributed irresponsibly.
Make it their problem, at their expense, and force them figure out how to solve