Mandatory insurance to cover what, exactly? On what basis would someone file a claim?
Insurance won’t cover murder.
Insurance won’t cover suicide.
There’s 95% of your gun deaths, right there. In the case of an accidental death, insurance will be profit incentivized to try and show that the accidental death was a suicide, and in many cases they might be true. (“kids, your daddy died while cleaning his gun” is codespeak for the unthinkable)
Establishments open to the public, such as gun ranges or hunting plots, are already insured.
So before you talk about insurance, you need to think deeply about what sorts of claims you want to insure. And once you’ve got that narrowed down, think about whether your proposed insurance program is going to fix anything that you’ve identified as a problem.