There are nearly twice as many guns in the average gun-owning household today as there were 20 years ago, according to new Wonkblog estimates based data from surveys and the Bureau of Alcohol, Tobacco, Firearms and Explosives. In 2013, there were an estimated 8.1 firearms in the typical gun-owning household, according to these data. In 1994, the average gun-owning household owned 4.2 guns.

These numbers comport with what survey research has shown for several years now: the share of gun-owning households has been declining over the past 20 years and possibly more, according to numbers from Gallup and the General Social Survey. On the other hand, domestic firearm production and imports of firearms have risen sharply, particularly in recent years. If those numbers are correct, it follows that increasing gun purchases are being driven primarily by existing owners stocking up rather than first-time buyers.

Plenty has been written about the decline in overall gun ownership rates. Many of these stories are based on the General Social Survey's data, which shows household ownership rates falling from over 50 percent in the 1970s to around 32 percent today. Some gun rights advocates dispute these numbers, preferring to use Gallup's household ownership rates instead, which have remained essentially flat over the same period.

But even Gallup's numbers show a decline in gun ownership since the early 1990s, from 54 percent of households in late 1993 to 43 percent as of this fall. And regardless of whether overall ownership rates are flat or falling, one thing that's largely been overlooked is how more guns and fewer gun owners means that firearms are being concentrated in fewer hands than ever before.

I calculated the per-household estimates as follows: I multiplied the total number of households in the U.S. (from the Census) by the share of households owning guns. Given the differences between the Gallup and GSS numbers on household ownership (something of a survey mystery), rather than pick one I used them both, to create high and low bounds for the number of gun-owning households.

I divided the total number of guns in the U.S. by the number of gun-owning households to arrive at an average number of guns per household. For the final number each year, I took the average of the estimate created by the GSS and Gallup household ownership rates.

Important caveat, as always: these are estimates built upon estimates, so there's a fair amount of wiggle room in the actual numbers. However, the overall trend of increasing guns per household is generally not in dispute. And the numbers comport with other estimates of the number of guns per gun-owning household, like a 2006 study finding that the average individual gun-owner owned 6.6 guns in 2004.

Also important: these are averages, which are a very blunt instrument for understanding the distribution of guns in the population. In all likelihood, there's a situation where a small percentage of gun owners own a huge number of guns, which brings the average up for everyone. For instance, that same 2006 study found that the top 20 percent of gun owners owned 65 percent of America's firearms. The top 3 percent of gun owners averaged over 25 firearms each.

For many owners guns are like tools, and you need different tools for different jobs: a rifle for hunting deer. A shotgun for hunting duck. A pistol for self-defense. An AR-15 for fun. Etc.

But in recent years, it seems many gun owners have seen fit to expand their toolboxes. There are probably a number of factors driving this: fear-stoking by some gun rights groups in the wake of mass shootings can lead to surges in gun-buying from existing owners concerned the government could take  their guns away. The rising popularity of "prepper" groups, who stock up on food and firearms in preparation for a variety of coming apocalypses, may also be playing a role.