The Obama presidency has been a boom time for the gun industry. Last Friday -- Black Friday -- was likely the biggest day in gun sales in American history. In March, we estimated that President Obama's tenure had already been a $9 billion boon to gun manufacturers. The reasons for this are many, but the president's focus on gun control has likely helped spur a rush for new weapons.

Our colleague Chris Ingraham noted another milestone that appears to have occurred under Obama: The number of guns in the United States is now larger than the number of Americans. This isn't a precise number, as we'll explain in a second, but here's how the relationship between the number of Americans and the number of guns has evolved.

The gray guns in later years are a function of that uncertainty. Historic data was compiled by Florida State University professor Gary Kleck in his 1991 book Point Blank: Guns and Violence in America and cited by The Truth About Guns in a look at the growth of gun ownership. Kleck's research was cited by the Congressional Research Service in its 2012 assessment of the number of guns in America (on which Ingraham based his analysis). Thanks to annual reports from the Department of Justice detailing the number of guns made, imported and exported each year, we can extrapolate outward from a number of points to estimate how many guns are in the United States currently.

U.S. regions differ in their concentrations of gun ownership. Here's what you need to know. (Osman Malik,Sarah Parnass/The Washington Post)

Using Kleck's numbers through 1987, a National Institute of Justice survey from 1994 (cited by the CRS) and CRS estimates for 1996 and 2007, we can generate a range of possible values for the number of guns in the United States, as below. In every case, the figure is now greater than the number of people in the United States.

(The gray guns in the animation are the difference between the low estimate, from the NIJ, and the high, extrapolating from Kleck.)

We'll note, as does Ingraham, that this ignores figures like the number of guns illegally exported, broken or destroyed each year. It's simply an estimate.

There's no question, though, that the past few years have seen a surge in the number of guns sold. As we noted earlier this week, 2015 had seen more background checks conducted by the FBI through October of any year since the background check system went into place.

In South Carolina earlier this year, law enforcement officials discovered a man with a cache of at least 5,000 firearms -- pistols, rifles, shotguns. It's not clear if he was simply a collector -- at extraordinary scale -- or someone trafficking in illegal firearms. It was probably among the largest collections of weapons ever seized by the government.

In 1955, it would have represented 1 out of every 33,000 guns in the United States. Nowadays, it's one out of every 63,600.

Icons used in the animation were created by Robert A. Di Ieso (the gun) and Alex Auda Samora (the person) and come from The Noun Project.