"free cam" won't work for turret mgs, because they use "ctrl" button for crouching. It's better to have ability to hide behind the gun than look around IMO. But there is way to do it, just code top mounted MGs like rear guns in planes, where you have ability to free look in limited way as long as you don't look through your sights. It's the only way to do it, but it's still better than nothing.