There's a huge risk for manufacturers selling big box/power retailers selling at low prices. The first being they can distroy the existing conduits to the consumer leaving the market in shambles taking away our buying choices. Second a sharp manufacturer wants balance in their customer base, they don't want to be owned one or two large customers who dictate terms of their business.
MAP (minimum advertised price) was divised to keep the big guy's in check as you can't control their selling price in their store but can control the advertised price and in store selling signage. This is the reason you see gun Ad's with POR (price on request) Anyone can advertise "we have the lowest prices or Our prices can't be beat" etc. Once in the store the seller can price his goods where he wishes, but if he embarresses the manufacturer with below market street prices there will be talks. As an example, a number of years ago a very large Outdoor retailer ignored a very large gun manufacturer's warning about advertising below MAP, they thought their size made them immune to the manufacturers MAP policy. The manufacturer pulled their product from the seller. The disagreement went to the lawyers. The manufacturer won.
Most factories supply the big boy's with a exclusive items for a given category. In the case of Walmart Federal supplied a once field load @ 1290 fps in 6, 7.5, and 8's that Walmart sold as a price leader while selling standard target loads at mainstream prices.
Many items on the shelf are considered convenice items and don't yeild high sales velocity so the margins aren't squeezed.
Bass Pro, Cabela's and others have made a business a big business selling fire arms and that's where their focus lies not in shot,wads, powder. These items are available at a price if you want or need them at that moment.
Surfer