In this July 20, 2014 photo, guns are displayed for sale at Dragonman's, an arms seller east of Colorado Springs, Colo. When Colorado lawmakers expanded background checks on firearms last year, they were expecting a huge increase. But the actual number the first 12 months of the law is far lower than projected, according to an analysis of state data by The Associated Press. (AP Photo/Brennan Linsley)

The FBI dealt with more background checks this Black Friday than ever before on the annual shopping day, according to a CNN report on Saturday.

Only once in its history has the agency had to handle a larger number of background checks in a single day: Friday, Dec. 21, 2012, exactly one week after the Sandy Hook school shooting.

All told, the FBI's National Instant Criminal Background Check System (NICS) ran more than 175,000 background checks on Friday. The agency typically handles about one-third of that on a more normal day, according to CNN.

The record number of requests for background checks isn't surprising. In fact, it's perfectly in line with recent trends. As HuffPost reporter Kim Bhasin wrote last year:

Gun-buying after Thanksgiving is becoming something of a holiday tradition. In each of the past two years, the Federal Bureau of Investigation has reported a record number of calls for background checks for gun purchases on the Friday after Thanksgiving. A flood of 154,873 calls on Black Friday in 2012, nearly three times the daily average that year, caused outages at some of the National Instant Criminal Background Check System's call centers.

But the growing number of Black Friday requests does present a challenge for the agency. By law, NICS has only three business days to complete a background check. After that, the decision to sell a firearm rests with the dealer.

As a result of that small window, the agency had roughly 600 of its employees logging long hours to make sure it completed as many background checks as possible on Friday. "No one is allowed to take leave today," Kimberly Del Greco, an FBI manager with NICS, told NPR on Friday. The FBI even asked some former employees to help with the workload, FBI spokesman Stephen Fischer told CNN.

As Philip Bump at The Washington Post notes, background checks are "an imperfect metric for approximating total gun sales." That's primarily because of two reasons: One background check can lead to the purchase of multiple firearms by a single individual, and certain individuals are able to purchase guns without a background check ever being completed because of the aforementioned three-days rule.

Nevertheless, the number of background checks being requested can be a useful indicator of general gun ownership trends. And according to the FBI website, all 10 of the top 10 highest weeks for background checks since 1998 have occurred in the past couple of years.