Because there is no national gun registry, the exact number of guns in civilian hands in the US cannot be determined, but a conservative estimate places it—as of 2010, when the gun-buying craze was just reaching its peak—at 270 million weapons. This was about 89 guns per 100 people, the most heavily armed civilian population in the world.
Another estimate, conducted by Congressional Research in 2012, places the total number of weapons in US civilian hands at 310 million as of 2009. By today, that means almost 1 gun for every single citizen, including infants. What would gun control even mean at this point? Assume this federal law from 2014 on, no more assault rifles. Those who already own one may keep theirs, but such weapons will disappear from gun stores and pawn shops. Have we controlled much of anything? There are still at least 3 million assault rifles out there.
In a perfect world, gun control would mean going house to house throughout the nation and taking away every single firearm, including muzzle loaders. That would be impossible. Regardless of its constitutionality, gun owners would either fight back until there were a nationwide civil war or simply hide their weapons and claim they have none. Since most of those in the US are unregistered, no one knows who has what. Owners could always claim they destroyed those that are