FBI background checks, the most reliable measure of gun sales, surged in December, capping a year that experienced strong growth in the last three months.

Background checks totaled more than 2.3 million in December, according to the FBI, compared to about 2 million in the same period in 2013.

While sales increased nationwide, there were sporadic reports of a spurt in people buying guns after local incidents of violence.

Related: Beretta wants to be U.S. Army's new gun. Again.

Gun shop owners in the St. Louis area, for instance, reported a spike in sales in the days following protests and rallies after a white police officer killed an unarmed black teenager in Ferguson, Missouri in August.

There was another wave of protests and riots in November after a grand jury declined to indict the officer, and gun shop owners again reported a spike in sales.

Background checks totaled more than 1.5 million in August, a considerable increase from about 1.4 million in the prior month.

Related: 2 guns a minute sold at $1 million

There was another pick up in October, to 1.6 million, and in November, to 1.8 million.

The December tally of 2.3 million, was bolstered in part by a strong holiday gun shopping season and a record Black Friday, when there was 175,000 background checks just on that one day.