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Attendees visit the trade booths during the National Rifle Association's (NRA) annual meeting in Louisville, Kentucky, May 21, 2016.
Aaron Bernstein—Reuters

Last year marked an all-time high for FBI background checks required for most firearm purchases. Gun sales toward the end of the year were extraordinarily brisk: The FBI processed a one-day record 185,345 background checks on Black Friday 2015, and soon thereafter the San Bernardino terrorist attacks inspired a surge of fear-related sales for bulletproof backpacks, vests, and of course, more guns.

A total of 23.1 million firearm background checks were conducted in 2015, the highest annual total ever. Yet even before the Orlando nightclub shooting last weekend left at least 50 dead, 2016 was on pace to supplant 2015's record.

As CNN noted, the FBI had handled 11.7 million firearm background checks through May 2016, compared to "only" 8.9 million for the same period in 2016. There is a long recent history of gun sales rising in the wake of mass shootings (see: Sandy Hook, San Bernardino), and the stock prices of gun manufacturers are already on the rise on Monday in the anticipation that the weekend tragedy in Orlando—the worst mass shooting in U.S. history—will result in another flurry of firearm purchases.

What's expected to be a fresh surge in gun sales comes soon after firearm giant Smith & Wesson reported a whopping 61.5% increase in revenue for the quarter that ended on January 31, 2016. February 2016 then went down as the third-biggest month ever for background checks despite it being the shortest month of the year, and and then March set a record high for the most ever gun sales for that month. April and May 2016 followed with all-time highs for those months, with 2,145,865 and 1,870,000 background checks, respectively, according to FBI data.

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While background checks are not required for every gun purchase, and some checks result in no sale because the would-be buyer is denied, FBI background checks are considered a ballpark proxy for gun sales in America. As many have noted with frustration and shock, the killer in Orlando was an American citizen who legally purchased the guns used in the attacks, despite being investigated by the FBI twice over alleged terrorism.