There's a reason our military uses 30-round mags and it's exactly as you explained. In combat, you need lots of ammo. People move around and even good shots will miss in combat situations. BTW: Not sure I'd be bragging about qualifying as a "Marksman." Unless things are different in the Air Force, Marksman was the lowest qualification level that was considered acceptable (Army). It ranked 3rd in the scale of badges (Marksman, Sharpshooter, Expert).