U.S. gun stocks came under fire on Monday after the latest National Instant Criminal Background Check System data from the for handgun background checks showed that almost 400,000 fewer checks run in April than in March.

Shares of American Outdoor Brands  AOBC, formerly Smith & Wesson, fell 2.4%, to $21.63 and Sturm Ruger  (RGR - Get Report) fell 2.1% to $59.19.

Mandated by the Brady Handgun Violence Prevention Act of 1993 and launched by the FBI in 1998, NICS is used by federally licensed gun dealers to determine if a buyer is allowed to buy a gun.

Before ringing up the sale, cashiers call in a check to the FBI or to other designated agencies to ensure that each customer does not have a criminal record or isn't otherwise ineligible to make a purchase.

The checks totaled 2,045,564 in April, down from 2,433,092 in March. 

Source: FBI
Source: FBI

The number of instant background checks increased markedly under the Obama administration as gun enthusiasts feared the former president would act to restrict outlaw firearms, which he did not do.

December of 2012, the first month after former President Obama's reelection, the FBI handlDs 2,783,765 checks, the most since the program's beginning.

President Trump aggressively courts the firearms lobby and The National Rifle Association and while campaigning came out heavily for gun rights. Trump's visit last week to the NRA is the first time since 1983 a sitting president has addressed the group.