Others have noticed this:
https://www.washingtonpost.com/news/won ... then-some/
A 2012 Congressional Research Service report published exactly one month before the Sandy Hook school shooting put the number of civilian firearms at 242 million in 1996, 259 million in 2000, and 310 million as of 2009.
If that 310 million number is correct, it means that the first year of Barack Obama's presidency was an inflection point: It marked the first time that the number of firearms in circulation surpassed the total U.S. population.
Philip J. Cook of Duke University suspects that estimates based on the ATF numbers don't properly account for this type of attrition. He's estimated that roughly 1 percent of the American gun stock gets destroyed, lost or broken in a given year. Applying that factor retroactively back to when the ATF first began keeping records in 1899, that would put the civilian firearm total at something like 245 million as of 2011, he said.
Other estimates downplay the effect of attrition. In 2007, the global Small Arms Survey estimated there were 270 million civilian firearms in the United States. Gary Kleck, a criminologist at Florida State University, says it's difficult to model the effects of attrition.
"Guns are simple machines made of extremely durable materials," he said in an e-mail, "yet are both dangerous and valuable enough that their owners would take more-than-average care to avoid losing them." His numbers produce an estimate nearly identical to the one in the chart above.
I did my own analysis based off 1946 production; where 1,533,365 guns were manufactured and the stockpile of guns in the US was estimated at 46,909,183.
Loss Rates (Fire/Theft/Flood/Etc)
0.30% -- 140,728 guns lost
0.40% -- 187,637 guns lost
0.50% -- 234,546 guns lost
0.60% -- 281,455 guns lost
0.85% -- 398,728 guns lost
1.00% -- 469,092 guns lost
It appears that a proper estimate for a loss rate is at the lower end around 0.30% of all guns each year; based off total production that year -- because guns are a semi-expensive durable consumer good -- it's expensive to manufacture them compared to other consumer items; and they last for decades if properly cared for; so you have to find the right balance between a 50 year old going "well, I lost my guns in the great flood of 1962, time to replace them" with new customers who just turned 18 and want a shotgun.
70 years with an average loss rate of 0.30% per year gives us a crude adjustment rate of 21%.
Applying that to the 362.16 million cumulative production stockpile adjusts it downwards to around 286.1~ million guns still floating around the USA.
If you wanted to drill down in more detail; you'd take into account a lower loss rate as we move into the "modern" era of around 1975 onwards.
One of the things you might notice in watching the recent Netflix 2019 movie "The Highwayman" with Woody Harrelson and Kevin Costner hunting down Bonnie and Clyde is the existence of gun racks sitting out in the open in people's houses in the 1930s.
People no longer drive around with gun racks in their truck rear windows; having switched to hidden safes or under seat gun racks. Same thing with houses -- more people have at least a cheap safe to keep firearms in which increases the probability of firearms surviving a catastrophic event, as opposed to "hang 'em up on the wall".