How much damage can a .308 round do?

My brother and I are having an argument on bullets and how much damage they'd do. For example, I believe that if you were shot in the shoulder with a .308, you could have your entire arm taken off. He says that the .308 is more for penetration, so it would just go through your shoulder leaving a clean hole. So would your arm be taken off? This includes using different rounds such as the premium HE rounds.