There are between 270 and 310 million guns in the US, according to estimates. Only 37% of those in the US admit to owning a gun. So, there could be vastly more than the estimates.

pewresearch.org

“Gun ownership is one of the hardest things for researchers to pin down (as the Pew Research Center’s Michael Dimock, among others, discusses here). A Pew Research Center survey conducted in February [2013] found that 37% of households had an adult who owned a gun — 24% said they owned a gun, and 13% said someone else in their household did.” More