Shares of Sturm Ruger were up 3%, while American Outdoor Brands, the company formerly known as Smith & Wesson, gained 4%. Both stocks have tended to rally in the immediate aftermath of mass killings, which sadly have become more routine.
WATCH LIVE: ABC News Special Report on the Las Vegas mass shooting
The Pulse nightclub in Orlando in June 2016. San Bernardino in December 2015. The Aurora, Colorado movie theater and Sandy Hook Elementary School in Newtown, Conn. in 2012.
Sheriff ID's suspect in Las Vegas shooting
Investors had bet that these massacres would lead to tougher gun control laws, especially because of tough talk from President Obama.
Eyewitness video from Las Vegas scene
The stricter laws never materialized. Instead, gun sales climbed during the Obama administration's two terms as gun aficionados bought more firearms just in case rules changed at a national level or in individual states controlled by Democrats.
Concertgoer: "I didn't want to die"
But shares of Sturm Ruger and American Outdoor Brands have both fallen sharply since Donald Trump, who was endorsed by the National Rifle Association, was elected president.
Woman describes Vegas shooting chaos on GMA
Investors had feared that a win by his opponent, Hillary Clinton, last year would have led to stricter regulations.
Trump's win removed those fears, and gun company sales and profits have plunged as a result. FBI background checks for firearms have fallen as well.
Sturm Ruger said in August that its latest quarterly revenues were down 22% from a year ago and that earnings plummeted more than 50%.
The company said that the main reason for the sales drop was "due to stronger-than-normal demand during most of 2016, likely bolstered by the political campaigns for the November 2016 elections."
American Outdoor Brands reported a nearly 40% decrease in sales during its latest quarter last month.
The weak gun sales are having an impact on the sporting goods industry as well.
Sales have plunged at Dick's Sporting Goods, and so has its stock. Shares are down 50% this year and the stock fell another 1% Monday.
Gun sales have also dropped at Cabela's, which was recently acquired by Bass Pro Shops. And Gander Mountain shut several stores this year after filing for bankruptcy.
Shares of Las Vegas-based casinos and hotels, including Mandalay Bay owner MGM Resorts, also fell Monday.
Meanwhile, stocks of leading casino operators fell on Monday after the horrific shooting in Las Vegas.
The gunman fired on a crowd at an outdoor country music festival from the 32nd floor of the Mandalay Bay hotel, killing at least 50 people, authorities said.
The stock of MGM Resorts International, which owns the hotel, was down 5% in premarket trading. Shares of Wynn Resorts and Las Vegas Sands Corp. were down about 1%.
Casino stocks have performed well recently, helped by Macau, a region of China that is a growth center for the industry. Wynn is up 70% this year, and MGM had been up 13% before the attack. MGM revenue had been up 19% this year.
Las Vegas attracted a record 42.9 million visitors last year, according to the convention and visitors bureau, up 18% from the recession year of 2009. The city has been on track for slightly less than that this year.
Vegas has lost some business as gaming options have grown elsewhere in the country and world, but it has still enjoyed a solid recovery.
Unemployment in metro Las Vegas was 5.2% in August, above the national average but down a half-point from a year ago. Home prices, hit hard during the housing bust, have nearly doubled from five years ago, although they're still far below their high during the housing boom.
Copyright 2017 Cable News Network. Turner Broadcasting System, Inc. All Rights Reserved.