Versions of the weapon are produced by several gun makers. Major retailers that sell guns in some of their stores, including Walmart and Dick's Sporting Goods, said they will restrict sales to those over 21 years old and make other changes to their policies. And several airlines, car rental companies and hotel chains have dropped rewards or discounts programs for National Rifle Association members. BlackRock, the world's biggest asset manager, has said it could use its position as the biggest shareholder of some gun makers to vote against directors or support shareholder proposals.