72 million gun owners seems low to me...
Here's a stat that pegs the total number of guns at around 434 million and just under 20 million AR-15s.
https://www.guns.com/news/2020/11/17/data-us-has-434-million-guns-20m-ars-150m-mags
At only 72 million gun owning homes, that would mean, on average, 6 guns per gun owner?
https://americangunfacts.com/gun-ownership-statistics/
22% of gun owners have only a single firearm. So if the 72 million number is correct, that means 15,840,000 single gun owners, and the remaining 418,160,000 guns are owned by 56,160,000, or 7.45 guns per owner.