In a single evening, and at the hand of a single man, shootings at Mandalay Bay in Los Vegas added more than 500 to the pool of Americans who have to be treated for gun injuries. The cost of these wounds cannot be calcuated. Beyond the financial expense, the societal and emotional expenses are difficult to imagine. But researchers have quantified one corner of the problem: hospital expenses. Gunshot wounds cost Americans $2.8 billion in hospital bills alone per year, according to a new analysis published in the journal Health Affairs, released coincidentally a day after the Las Vegas attack....