Free: I think 500 million is a pretty accurate guess. I suspect there are very few gun owners that have just one firearm. My estimation is based on the following:
1. Pistol for husband
2. Pistol for wife
4. Deer rifle
5. Plinker .22 especially if kids in household.
I also wonder how many pellet guns are out there. I’ve never seen an estimate on those. Anyone have a guess?