(Alex Brandon/AP)

On Monday afternoon, while the attention of the political media world was focused on events at the United Nations, the Bureau of Alcohol, Tobacco, Firearms and Explosives announced that it was dropping plans to reclassify a particular form of ammunition. It was a rare success for a letter-signed-by-most-Republican-senators this week, after Sen. Chuck Grassley (R-Iowa) got most of his colleagues to sign on to a missive that captured an already-bubbling sentiment among conservatives. (That opponents of gun control measures won a victory, of course, is anything but a rare success.)

If you want the full back story, it's here. But what we want to focus on is the phenomenon that has frequently resulted when the administration has either threatened new gun control measures or when the public has been worried that it might, as it did in the wake of the ATF's recent announcement: Firearm sales skyrocket.

As soon as Barack Obama won the 2008 election, gun sales spiked. The number of background checks (a point of data linked to gun sales numbers) increased by 50 percent over the rest of that year in November and December. (December figures are often higher, we'll note, due to the popularity of giving weapons as Christmas presents.) The Aiken Standard in Aiken, S.C., wrote about spiking sales that December, quoting an employee at a local gun store: "There's been a definite increase. It's because a Democrat is in office, in my opinion." Not quite in office, but you get the point.

To measure how big the Obama Gun Boom has been, we turned to the National Shooting Sports Foundation. It uses data on excise taxes collected by the government on weapon and ammunition sales to estimate the total market for those products. It provided its estimates from 1982 through the third quarter of last year to the Post.

Overall, the estimates look like this. We've shaded in the Obama Era as encompassing 2008 through 2014, due to the spike at the end of 2008. (That plays into our projections later, so bear that in mind.) Notice the spike in 1993, as well, the last time a Democrat assumed the presidency. And, of course, backed the Brady Handgun Violence Prevention Act, which is precisely the sort of thing gun advocates fear.

If you adjust those figures into 2014 dollars and look at them by quarter (to eliminate the gap in 2014 data), the per-quarter estimated total sales of firearms and ammunition look like this. That spike in the Obama era is no joke.

To figure out how much better the industry was doing in the Obama years, we did a simple linear trend analysis based on quarterly data from 2003 to 2007. What might have been expected, had those trends continued, is the light red section of the graph below. What actually happened is the dark red part to the right of the gray line: the Obama Boom.

How much was that boom worth? If you calculate out the difference between what might have been expected and what was, it's about a $10 billion increase through the third quarter of last year. Much of that came in late 2012 and early 2013, when gun advocates were worried about new control measures in the wake of the the Newtown shootings. Part of it, too, is linked to rumors in the middle of 2013 that the government was stockpiling ammunition, causing something of a run on ammo in the private sector. (For the sake of completeness: If you use the 2004 to 2008 period to do the trend projection, the total increase due to Obama would only be about $2 billion since there was the upward tick at the end of 2008.)

If we do similar projection by type of sale, you can see how the actual estimates from the NSSF compare to our projection.

If you add these figures up, by the way, it comes out to about $9 billion since 2008 -- mostly a function of the conversion factor we used versus the one the NSSF used.

The entire point of this exercise, of course, is that there was another jump in ammunition sales in the wake of the ATF proposal. The $9 to $10 billion in increase under Obama will keep growing, through the end of 2016. At which point gun manufacturers will probably be sad to see  Obama go -- even if gun buyers are not.