923, I'm not sure how insurance would have the impact you state. I agree with your send point re: SCOTUS, but I'd be interested in further comment from you on the first point.
i have commented at length in other threads (especially the omnibus gun violence thread). First, if you have to insure every gun you own, people would be deterred from owning a bunch of guns. This - over time - reduces the number of guns in circulation.
Second, because guns are inexpensive, the cost of insurance would be a significant part of the overall cost of ownership, and people would be motivated to keep their costs down. Private insurance companies would lower their rates for people who have approved gun safes - and might outright require gun safes or other safety devices as a condition of insurance. That would increase the use of gun safes and locks and might make it more difficult for some of these kids who get their parent's guns, and might have some impact on suicides as well.
Third, insurance companies would also require or at least reward training for their insureds. This could also impact the rate of accidental shootings over time.
Fourth, if a gun is stolen, people would be more likely to report it because they would not want to pay insurance on a gun they no longer have.
Fifth, insurance would require some documentation of transfers so the new owner pays the insurance. This would reduce the number of untraceable guns out there, and also reduce gun transfers from responsible older gun owners to irresponsible young people who might use them in crime or sell them on the street.
Let me make clear that all of this is on the margins. I think there would be a real impact but it would be relatively small. The best way to stop gun rampages is to greatly restrict the ownership of guns, as seen by, oh I don't know, every other industrialized country. But since we have the Second Amendment, that's not an option and this is the only proposal I have seen that might actually do some good without being unconstitutional.