CAMBRIDGE, Mass. — In between completing problem sets, writing code, organizing hackathons, worrying about internships and building solar cars, a group of MIT students make their way to the athletic center, where they stand side-by-side, load their guns and fire away. They are majoring in biological engineering, brain and cognitive sciences, aeronautics, mechanical engineering, computer science and nuclear science. Before arriving at MIT, nearly all of them had never touched a gun or even seen one that wasn’t on TV. “Which is strange because I’m from Texas,” said Nick McCoy, wearing a T-shirt advertising his dorm and getting ready to...