By Noel Randewich

SAN FRANCISCO, Feb 28 (Reuters) - For years, the shares of gunmakers have tended to climb in the wake of mass shootings, but the second-deadliest shooting at a public school in U.S. history may have changed that.

Since the killing of 17 students and staff at Marjory Stoneman Douglas high school in Parkland, Florida, on Feb. 14, there has been an outpouring of calls for gun control measures. And the shares of firearms makers Sturm Ruger & Company and American Outdoor Brands, the maker of Smith & Wesson, have slumped more than 14 percent.

On Wednesday, Sturm Ruger fell 6.6 percent and American Outdoor Brands fell 3.2 percent after Dick's Sporting Goods, which sells their firearms, said it would permanently halt sales of assault-style rifles like the AR-15 used at Stoneman Douglas.

The school shooting reignited a fierce debate over gun safety. Protests by social media-saavy student activists and calls for company boycotts have grabbed the national spotlight, while rattling large money management companies that own shares in gunmakers like never before.

BlackRock, the largest shareholder in both American Outdoor Brands and Sturm Ruger, last week announced it would speak with manufacturers and distributors “to understand their response” to Parkland.

"That has prompted concern within the investment community that there could be some changes, and that has resulted in some near-term selling pressure," said Aegis Capital analyst Rommel Dionisio, who covers firearms makers.

Wall Street rewarded Dick's Sporting Goods with a 0.69 percent price increase after the retailer said it would stop selling assault-style rifles and high-capacity magazines, and that it would not sell any guns to people under 21.

The recent sell-off in gun stocks represents a break from share moves following other mass shootings in recent years. Calls for stricter regulations following many of those shootings pushed firearm stocks higher due to expectations that people might stock up on guns in anticipation of stricter rules.

After the deaths of 14 people in a shooting in San Bernardino, California, in 2015, America Outdoor Brands' stock surged 25 percent over five sessions. After a gunman killed 49 people at the Pulse Nightclub in Orlando, Florida, in 2016, the stock rallied 14 percent over five sessions.

Not all mass shootings in recent years have been positive for gun stocks, however. After a man killed 26 people, including 20 children, at Sandy Hook Elementary School in Newtown, Connecticut, in December 2012, American Outdoor Brands fell 13 percent in five sessions.

YOUTH-LED WAVE

Federal Bureau of Investigation background checks - an industry proxy for U.S. gun sales - hit a record high that month, and America Outdoor Brands' stock recovered its losses in January.

Expectations of new gun control measures grew more as Democratic candidate Hillary Clinton appeared likely to win the 2016 U.S. presidential election. That helped propel American Outdoor Brands' stock to a record high.

But following the election victory of Republican Donald Trump, who opposed gun control, expectations of regulation fell. American Outdoor Brands has lost half of its stock market value under Trump, while Sturm Ruger has fallen 16 percent.

The Springfield, Massachusetts company, whose stock rose the day after the most recent Florida shooting before steadily tracking lower, is expected to show a 26 percent slump in revenue when it provides its January-quarter report after the bell on Thursday.

Following a youth-led wave of protests, along with proposals from state and national officials to pass stricter regulations, investment heavyweight Blackstone Group last weekend asked funds it invests in for details about their stakes in companies that manufacture or sell guns, according to the Wall Street Journal.

Adding to the pressure, New Jersey legislators have said they plan to introduce bills to bar state pension funds from investing in gun manufacturers.

While gunmakers' shares have been hurt by investors' and companies' responses to recent calls for gun regulation, sales of assault-style rifles might be up, following the pattern seen so often in the past.

R&R Gun Shop in Sebastian, Florida, in recent days has sold out of its AR-15s, said co-owner Roberta Wilson.

"Everyone wants one because they're afraid they're going to ban them," Wilson said. "We can't get any."

(Reporting by Noel Randewich Editing by Tom Brown)