2017 saw the second-most gun-related FBI background checks on record, a report released on Wednesday showed.

The National Instant Criminal Background Check System (NICS) conducted 25,235,215 checks last year. That's nearly 2.3 million checks fewer than the record-breaking year of 2016 but also nearly 2.1 million checks more than 2015, the third-best year on record.

The number of checks conducted by NICS is generally considered a leading indicator of how many gun sales have been processed in a given period of time in large part because nearly all sales—including all new gun sales—made through a federally licensed dealer must include a background check. It is not, however, a perfect representation of raw gun sales for a number of reasons. Sales between private parties on the used market are not required to go through a background check in most states. Sales of multiple guns during one transaction generally only require a single background check.

"These statistics represent the number of firearm background checks initiated through the NICS," the FBI wrote in its report. "They do not represent the number of firearms sold. Based on varying state laws and purchase scenarios, a one-to-one correlation cannot be made between a firearm background check and a firearm sale."

The National Shooting Sports Foundation, a leading industry group, also pointed out that NICS check numbers reported by the FBI include checks for gun-carry permits. The group's own analysis of the report found 2017 was the fourth-highest year on record for gun checks. They said the slow down compared with 2016 was expected but considered 2017 a historically strong year regardless.

"On an NSSF-adjusted basis, we are looking at the fifth-highest December, fourth-highest Q4 and fourth-highest year," Michael Bazinet, an NSSF spokesman, told the Washington Free Beacon. "Ahead of a presidential election in which one presidential candidate promised more gun control on the federal level, 2016 was an all-time record year and no one in the industry expected a repeat of that. Even so, 2017 was a good year on an historical basis showing underlying strength for the shooting sports and for Americans wanting to exercise their Second Amendment rights."

Alan Gottlieb of the Second Amendment Foundation said the political implications of a potential Hillary Clinton presidency played a large role in 2016's record-breaking numbers that faded after Donald Trump won the election.

"Gun sales were down from 2016 because the threat to gun rights, which drives demand, was no longer being driven by attacks on gun ownership from Barrack Obama and Hillary Clinton," he said.

Gottlieb said he expects sales to remain near historic highs in the coming year: "I think sales of firearms in 2018 will be close to levels in 2017 due to threats on gun rights on the state level and the continued concern for keeping safe from crime and terror."