April 2018 saw the most gun-related checks run through the Federal Bureau of Investigation's background check system.
The National Instant Criminal Background Check System (NICS) ran 2,233,213 checks in April, according to an FBI document. That's nearly 90,000 more checks than the previous April record set in 2016. It also represents the second month in a row to set a record with March seeing 2,767,699 checks.
The drop off in background checks between March and April matches the industry's typical sales cycle where more guns are sold in winter months than in summer months. December tends to be the best month for gun sales in any given year. December 2015 holds the record for most checks in a month with 3,314,594.
NICS checks are one of the strongest indicators of gun sales in the United States. While there is no federal registry of firearms, NICS checks are required on nearly all sales conducted by licensed gun dealers. The number of checks does not perfectly correlate with the number of gun sales, though. Most states do not require NICS checks for sales of used firearms between nonlicensed individuals, many states use the checks during the gun-carry permit application process, some states don't require a NICS check during sales to those with gun-carry permits, and multiple guns can be sold during a single NICS check.