I'm no fan of Walmart, but somehow they manage to get $100+ a week of my money.
Anyhow, I buy ammo there on occasion. Most of my shooting is done with my reloads, or rimfire bought by the case over the internet. As far as I know, and I'd bet money I'm right, there is no difference between the box you'd buy at Walmart, the box you pay double for at a big box store, or the box you pay triple for from your local Mom and Pop gun shop. The reason Walmart's is less expensive is because they buy it by the truck load, not by the case as your local gun shop does. Walmart does not sell "seconds" of ammo. Same for the Walmart stores that sell guns. They don't sell "seconds". They buy thousands of guns at a clip, literally a truck load of say, Ruger 10/22 rifles, then distribute the guns themselves between their own stores. Your local gun shop may order 3 maybe 4 Ruger 10/22s at a time, and have to pay more per gun than Walmart does.