Semi-automatic AR-15's on display. Getty Images

Mr. Stack said he hoped that conversation would include politicians. As part of its stance, Dick's is calling on elected officials to enact what it called "common sense gun reform'' by passing laws to raise the minimum age to purchase guns to 21, to ban assault-type weapons and so-called bump stocks, and to conduct broader universal background checks that include mental-health information and previous interactions with law enforcement. Mr. Stack said the retailer began scouring its purchase records shortly after the identity of the suspected Parkland shooter, Nikolas Cruz, became known. The company soon discovered it had legally sold a gun to Mr. Cruz in November, though it was not the gun or type of gun used in the school shooting. "But it came to us that we could have been a part of this story,'' he said. "We said, 'We don't want to be a part of this any longer,'" said Mr. Stack. That decision raised rounds of discussions with top executives inside the company as well as the directors, all of whom backed the decision to take a stance, said Mr. Stack.

As of Wednesday morning, the company said all AR-15s and other semiautomatic rifles would be removed from its stores and websites. Mr. Stack said Dick's remained a staunch supporter of the Second Amendment and will continue to sell a variety of sport and hunting firearms. Although he has never been a member of the N.R.A., Mr. Stack said he is, in fact, a gun owner and enjoys trapshooting clay targets. But when it comes to selling guns to individuals under 21 years of age or stocking assault-style rifles, Mr. Stack said his company was done. "We don't want to be a part of a mass shooting," he said. This is not the first time Dick's has made changes in response to a school massacre. In 2012, after the shooting at Sandy Hook Elementary School, Dick's removed assault-style rifles from its main retail stores. But a few months later, the company began carrying the firearms at its outdoor and hunting retail chain, Field & Stream. This time, Mr. Stack said, the changes will be permanent. Dick's planned to inform its employees of the new policy in an internal note Wednesday morning, shortly after Mr. Stack appeared on "Good Morning America" to discuss the decision. Dick's is not the first retailer to stop selling the semiautomatic guns. In 2015, Walmart said that it would no longer sell high-powered rifles in its stores in the United States. But Walmart sidestepped any controversy involving gun politics, attributing its decision to lower customer demand for the military-style rifles. It is unclear what financial impact the decision will have on Dick's business. Neither Dick's nor its competitor, Cabela's, now owned by Bass Pro Shops, have broken out firearm sales in their financial reports. But last August, Dick's shares plummeted after it said weak results from its hunting segment resulted in its missing Wall Street's second-quarter earnings estimates. Over all, firearm sales for retailers and gun manufacturers have slumped since Donald J. Trump was elected president, as fears of stricter gun regulation receded. Firearm sales data for the United States is not readily available, but background checks tumbled more than 8 percent last year, the largest fall since the F.B.I. began keeping track in 1998. Mr. Stack said he and his company expected there would be mixed response — including fallout — to its new policy. "The whole hunting business is an important part of our business, and we know there is going to be backlash on this," said Mr. Stack. "But we're willing to accept that." He added, "If the kids in Parkland are being brave enough to stand up and do this, we can be brave enough to stand up with them."

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