The USA has about 254 million adults, and the estimated number of guns is 400 million (about 1.57 guns per resident).

Forty percent (abt 101 million) say they live in a house with a gun. Thirty percent (abt 76 million) say they own at least one gun.

The US death rate is about one percent for all ages, so by simple extrapolation, (0.01 X 75MM =) 760,000 gun owners die every year, and they own 1,193,000 guns.

No state as far as I know regulates the posthumous transfer of weapons. Most of the gun owners I know have them strewn about the house, loaded, with minimal controls on access. Most of those I know well are seniors, and most of those are intimately familiar with the decline of short-term memory, as in "where did I leave my keys?" or "why did I come into this room?" for example.

We can therefore assume that each year about a million guns are scattered, forgotten or lost, and that most, unwanted by the 70 percent who don't own guns, just drift into the pool of loaded, rusting and deadly trash piling up in basements, barns and landfills across the country, waiting for the child, the disturbed and the cowardly to find them.