I'm extremely skeptical of any stats around firearm counts, and ownership stats. Firearms aren't registered, which means the only data we have are the amount of background checks for buying them from a dealer (which goes through a department at the FBI called NICS). The issue is:

+ Those background checks are used for lots of things other than firearm purchases

+ Firearms can be transferred legally in some cases without background checks

+ Plenty of firearms existed before the background check system and are still owned and functioning

+ Many firearms are purchased, left to rust or otherwise break, and never repaired.

+ Firearms are occasionally turned in to the police or surrendered (usually when a family member passes and their relatives don't know what to do with the firearms).

The other source of information is directly asking people, but that runs into a bunch of problems too, mostly that people will lie.

I also don't think there's any kind of remotely common pattern that lets us correct this bad data from self reporting. Liberal gun owners are likely to lie about owning a firearm since they don't want their family to know, and conservative firearm owners are less likely to trust the person they're reporting to. Many firearm owners are taught to never ever talk about being a firearm owner to avoid being a target for burglary.

My point is, we simply don't know at all. Any gross figure is extremely suspect.