He added that Wal-Mart shoppers "were buying shotguns and rifles, and so we are increasing assortment in that."
Lundberg tells NPR the move is happening now because of the change in seasons:
"As our Sporting Goods departments are resetting this week from Summer to Fall, the MSRs are being taking out of the assortment and replaced with new rifles and shotguns."
The soon-to-be phased out AR-15 was used in several high-profile shootings over the past few years, including the 2012 shooting at Sandy Hook school in Newton, Conn., and the movie theater shooting in Aurora, Colo. Gun control advocates support bans on these types of weapons and welcome Wal-Mart's decision to remove them from the shelves.
"The AR-15 is America's most popular general use rifle," Hunter told NPR.
In Hunter's emailed statement, the NRA called Wal-Mart's recent move disappointing.
"While we're disappointed in Wal-Mart's decision, we appreciate the firearms retailers who continue to carry these firearms and enable law-abiding citizens to purchase the firearm of their choice."
In 2006, Wal-Mart also cut back on gun sales, removing firearms from about a third of its stores, again chalking the decision up to "diminished customer relevancy." But then in 2011, it reintroduced guns to more stores around the country.
According to CNN Money, a Wal-Mart spokesman said at the time that the retail giant "realized there is broader appeal for guns in some areas because of sporting needs."
Wal-Mart will be selling the discontinued rifles at steeply discounted rates as it phases them out.
Correction Aug. 28, 2015
An earlier version of this post included a photo of a weapon that was not an AR-15.