The company, which operates more than 715 locations, already had pulled assault-style weapons from Dick's stores after the 2012 Sandy Hook shooting; now it will also stop selling the weapons at its subsidiary Field & Stream stores.
Stack said the decision to eliminate assault-style rifles is permanent.
"Our thoughts and prayers are with all of the victims and their loved ones," the company said in a statement issued Wednesday. "But thoughts and prayers are not enough. We have tremendous respect and admiration for the students organizing and making their voices heard regarding gun violence in schools and elsewhere in our country.
"We have heard you. The nation has heard you. ... The systems in place are not effective to protect our kids and our citizens."
The statement asserted the company's support for the Second Amendment but continued, "we have to help solve the problem that's in front of us. Gun violence is an epidemic."
In addition to changing its own policies, the company issued a plea to elected officials to enact "common-sense gun reform," specifically calling for the following regulations:
- Ban assault-style firearms
- Raise the minimum age to purchase firearms to 21
- Ban high-capacity magazines, as well as bump stocks — gun accessories that allow semi-automatic rifles to operate like fully automatic weapons
- Require universal background checks that include relevant mental health information and previous interactions with the law
- Ensure a complete universal database of those banned from buying firearms
- Close the private sale and gun show loopholes that waive background checks
With their moves, Dick's and Walmart join a host of major companies that made changes in reaction to the Parkland shooting. As NPR's Amy Held reported last week, many other high-profile companies -- from MetLife Insurance and First National Bank of Omaha to Symantec and Hertz -- have ended their corporate partnerships with the National Rifle Association.
Those moves have not been without controversy.
Earlier this week, for instance, Georgia Lt. Gov. Casey Cagle threatened to "kill any tax legislation that benefits" Delta Air Lines after the company ended its own relationship with the NRA. Delta, which is based in Atlanta, had announced two days earlier that "we will be requesting that the NRA remove our information from their website" -- a decision Cagle described as an attack on conservatives.
Asked about the potential for pushback among gun rights advocates, Stack acknowledged the move "isn't going to make everyone happy. But when we look at what those kids and the parents and the heroes in the school, what they did, our view was: If the kids can be brave enough to organize like this, we can be brave enough to get these [firearms] out of here."
"We're staunch supporters of the Second Amendment," he added. "I'm a gun owner myself. We've just decided that based on what's happened and with these guns, we don't want to be part of this story."