Close, but the best estimates are there are 470 million guns in US civilian hands.

That’s the the lower boundary. The real number is probably closer to a billion.

You have to remember that untold millions of firearms were sold before anyone really started keeping track, no federal authority was keeping track before 1968ish, and that firearms will easily last a century if they are not fired too often and given even a minimum amount of care.

I myself inherited several pre-'68 firearms that would never have been counted. My 90 year old father in law has a dozen or more that he inherited or bought (western ranching family) that are still functional despite being manufactured over a century ago!

To put a fine point on the issue; into the 1970’s you could buy firearms off the shelf at hardware stores or even CoD via mail order. 470 million is a low number.