That's a lot of guns, but your statistics aren't applied properly and are misleading. Actual gun ownership is confined to about 30% of citizens, down from over 50% in 1973, when percent of gun ownership peaked. Percent of gun ownership in the US has declined since then while the number of guns has risen. If US population is 325 million and 30% own guns, then 97.5 million people own an average 3.38 guns apiece. Of course, a lot of people own a lot of guns, including more than 3 million National Firearms Act registered weapons including nearly a half-million registered machine guns.    http://www.theblaze.com/news/2013/03/19/how-many-people-own-guns-in-america-and-is-gun-ownership-actually-declining/
And for two centuries, the Supreme Court basically left firearms possession up to local law.