Gun ownership involves risk and the potential for damage that incurs real expense. As with automobiles and other possessions that embody risk, owners of firearms should be required to purchase liability insurance to help offset any damage that may occur as a result of their use.
In this scenario, responsible, law-abiding citizens who own 'reasonable' guns and keep them in safe places (e.g., away from children) would pay very little.
Those who want to own an assault weapon, amass an arsenal and pack heat in public would pay more because they pose a greater risk of inflicting damage.
Private insurance companies will work out the actuarial risk assessments, removing the government and 'the 2nd amendment' somewhat out of the equation.
A simple, market-driven solution.