It's neat that you happened to be there when they unloaded that.
Around here, we've got two Wal Marts. One is in the Denver district and the other one is in the Salt Lake City district. So you can drive across town and find fairly different store stock and even policies.
Anyhow, on the east side, they used to sell the Fed 510B in bricks of 500 rounds as well as in boxes of 50. For years the price was $1.47 per box of 50, or 14.70 for a brick. Then they raised their price to, I believe, $1.97 per box of 50.
On the west side, they NEVER sold the 510B by the brick. They always broke the bricks down and sold it by the box. But the pricing was the same, and the price went up at the same time in both stores. (That was a couple of years ago). I stopped buying the 510B when the price went up. Why pay $20 a brick for the 510B at WM when I could (at that time) get Blazers at Sportsman's Warehouse for $16 per brick, and I didn't have to wait for the keymaster nor be limited to three boxes. If you wanted to fill up a shopping cart, nobody cared.
Ahhh. The good old days.

So when the WMs here had the six box limit a few years ago, you could walk into the east side store, and if they actually had 510B in stock, you could theoretically have bought 6 bricks of the stuff in one visit.
On the west side, you'd have been limited to six 50-round boxes simply because they always insisted on taking the bricks apart. I always thought that was kind of odd.
Many people have excellent luck with the 510B. I have had OK luck with it from most guns, but it doesn't cycle some semi-auto pistols well in my experience.
If you found 510B for $14.70 per brick, and were allowed to buy three bricks, that was an excellent score, in my opinion. That's what I like to see! :bthumb: