David Hogg, one of the high school students from Parkland, Fla., who have been pushing a gun-control campaign since the shooting deaths of 17 classmates and staffers and the wounding of dozens more, urged investors Wednesday to let big investment firms know if they oppose investments in U.S. gun manufacturers, and to "#BoycottVanguard" and "#BoycottBlackRock" for their gun investments.

BlackRock owns 11 percent of American Outdoor Brands Corp., which controls the firearms maker Smith & Wesson; 13 percent of Sturm, Ruger & Co.; and 13 percent of Vista Outdoor. Vanguard owns 8 percent, nearly 10 percent, and 9 percent of the three companies, respectively, according to Securities and Exchange Commission filings.

Activists have pressured companies including the insurers Chubb and MetLife, car rental and consumer software companies to stop special discounts for members of the National Rifle Association, which has opposed many gun-control initiatives.

Hogg and his fellow students have been leading a nationwide movement to end gun violence. And Hogg triggered a successful advertiser boycott last month of  Laura Ingraham's Fox television show after she openly ridiculed his college rejections.

In his social-media postings this month, Hogg noted that Vanguard and BlackRock “are two of the biggest investors in gun manufacturers; if you use them, feel free to let them know.” Hogg’s Twitter handle, @davidhogg111, claims 765,000 followers.

As managers of the nation's largest stock-index funds, Vanguard and BlackRock own at least 5 percent each of most widely traded U.S. companies.

BlackRock says it owns the three gun-makers only in its stock-index portfolios, and that it's thinking about starting "social criteria" funds that don't include gun stocks.

After the Parkland slayings, BlackRock posted a statement that it was "pursuing" talks with the three companies and had asked at least one, and planned to ask the others, to detail how they measure and manage "reputational, financial and litigation risk."  This ranges from making guns to how they "support the safe and responsible use" of guns, how their guns are sold, whether they are often sold to criminals, and whether they are investing in trigger locks and other gun-safety technology. BlackRock's iShares exchange-traded funds (ETFs) have gone a step further, setting up "firearms-free" investment funds for investors who don't want to own gun stocks.

Vanguard didn't respond to a request for comment. In a meeting with investors last fall, Vanguard's new chief executive, Mortimer "Tim" Buckley, said even those investors who claim interest in social-criteria investments have so far showed little inclination to buy funds that exclude classes of stock on environmental, social, or governance grounds. "You are taking the social morals of some and imposing it on the people. You can never get them to agree," Buckley said at the time.

BlackRock and Vanguard are also major owners of Dick's Sporting Goods, which said it would stop selling rifles after the Parkland slayings. Vanguard and BlackRock each own around 8 percent of Dick's shares.