I worked at an Academy, and there were 3 - 4 Bushmaster's on the shelf, 1 - 2 Remington, and usually about 2 S&W's in the gun rack at any one time.
In addition to the Beretta CX4 Storm's, with about 4 - 8 locked up behind the cage, and the store right down the road had more AR-15's and Sig 556's.
Sportsman's Warehouse, on the other hand, had everything from M1A's, AR-15's, Sig 556's, etc. Now, San Antonio ain't the same as New Orleans, but it's entirely possible that there are that many AR-15's. Whether or not that twenty of them were sold, it takes about 10 minutes to fill out a 4473 if you know what you're doing, about another 5 minutes to call NICS, get a proceed, and then another 5 minutes to log it into the computer and get a manager to approve it then walk it up to the cash register.
As far as ammo goes, we usually stocked Monarch in .223, and had about two cases of ammo on the shelf and about another 4 sitting on the warehouse racks.