In an effort to fire up slumping sales, Walmart is bringing guns and ammunition back to many of its U.S. stores. Here, a quick guide to the retailing giant's decision:

What is Walmart doing?
It is "quietly" reintroducing shotguns, hunting rifles, and bullets in about 500 of its nearly 3,600 locations.

Wait, hadn't Walmart stopped selling firearms?
Not entirely. It stopped carrying firearms in all but 1,300 of its U.S. locations in 2006, citing low sales. And it remains the largest seller of firearms and ammunition in the U.S. Walmart did stop selling handguns in all stores except Alaska outlets in the 1990s.

Why now?
The move comes "as part of a larger push to restore 'heritage categories' of merchandise such as fishing rods and bolts of sewing fabric that it removed in an attempt to go upscale," says Miguel Bustillo in The Wall Street Journal. That attempt "backfired" and sales at Walmart's U.S. stores have slumped. The chain also says it realized the appeal of guns may have been "broader" than it thought.

How are gun-control advocates responding?
An anti-gun coalition in New York City is pushing Mayor Michael Bloomberg to reject the retailer's plan to open up stores in the Big Apple. The city needs to "take a hard stand against Walmart's decision and make it clear that any corporation that looks for new markets to sell guns and fosters a culture of violence is not welcome in New York," says Manhattan Borough President Scott Stringer, as quoted in The New York Observer.

Sources: CNNMoney, The Consumerist, MarketWatch, New York Observer, Wall Street Journal