I think I read somewhere that there are more privately owned firearms in the US than every military in the world...combined.
There was another article showing private ownership of ammunition in the 10s of billions of rounds.
They base these numbers n NiC and manufacturing estimates
Have seen a reliable source that estimates probably twice that number in actuality considering the lack of records not that many decades ago
Also that there are probably 20+ million firearms that are lost, forgotten or packed away that no one knows where they are