What we need is a system which locates the costs which guns generate in society with those in a position to reduce those costs. We need to stop forcing the taxpayer to pay the costs and indemnify bad behavior.
Therefore we should just simply add up the unrecovered costs from the prior year(s*) and then place a tax on guns and ammunition which would recover those costs. Those who buy, sell and use guns would have a powerful incentive to keep the taxes as low as possible so that they would change their behavior in fact to reduce the deaths and maimings, and not just fantasize that they have done so, like they do now. Their attention would be focussed on effective methods not just plausible excuses for why it isn't their problem.
How to keep guns out of the hands of the mentally ill or emotionally uncontrolled, is their problem. As it should be. They want high-capacity magazines? They can have them. If high-capacity magazines have no effect on the number or severity of mass shootings, in fact, then they will enjoy the benefits. If they do have an effect then they have a means of reducing costs.
yrs,
rubato
* We can use a running average.