If anyone is coming for America’s guns, they’d better get a move on, because bullets are in short supply. Gun enthusiasts are buying up ammo like it’s going out of style, leading to massive shortages for big retailers like Wal-Mart and Cabela’s, and a near-drought for local gun dealers. As demand increases, prices have nearly doubled. It’s a particularly interesting phenomenon, as recent studies show that gun ownership is on the decline across the country, meaning that people who do own guns are buying more of them, and making sure they’re stocked with plenty of ammo …