Wartime U.S. presidents have taken keen personal interest in picking the most lethal gun for the military. But in President Obama's first foray into small-arms procurement for the armed forces, his Jan. 4 executive order on gun control directs the Pentagon to find ways to make not so much more lethal firearms, but safer ones. His direct order has brought a few snickers among retired combatants who argue that the commander in chief is issuing his directive at a time of more pressing small-arms priorities. The military, critics say, fields a flawed personal rifle and has spent more than a...