Some of Wall Street's largest exchange-traded funds are currently invested in American Outdoor Brands — formerly Smith & Wesson — and Sturm, Ruger & Co. , designers, makers and retailers of firearms for domestic buyers.

Last week's mass killing of 17 people at a public high school in Parkland, Florida, has caused some major pension funds and institutions to investigate the extent of their investments in gun makers.

Fierce scrutiny has pushed New Jersey state lawmakers to restrict the state's public pensions from investing in the stocks of gun manufacturers, while the world's largest asset manager, BlackRock, said it would "engage" with the companies on their response to the shooting.

To be sure, while each fund in the list contains shares both of American Outdoor Brands and Sturm, Ruger & Co., the gun stocks tend to comprise a very small fraction of the entire fund, less than 1 percent of the entire portfolio.

The funds on the list are largely "passive." That is, they are investors in the stocks because the shares are members in certain indexes tracking the economy. There isn't a manager making a conscious decision to buy the gun makers for these funds; they are invested in the stocks because these companies are in the appropriate index mimicking a part of the U.S. economy.

— CNBC's Chris Hayes contributed to this report.