//cameraRayVector - взят Getpoint с луча у камеры
//gunRayVector - взят Getpoint с луча у пушки
//vAngle - находим угол между векторами, отнимаем от каждого вектора позицию камеры, для того чтобы угол считался не с нулевой позиции координат  
float vAngle = Vector3.Angle((cameraRayVector - _mainCamera.transform.position), (gunRayVector - _mainCamera.transform.position));

                           Vector3 cross = Vector3.Cross((cameraRayVector - _mainCamera.transform.position), (gunRayVector - _mainCamera.transform.position));
                           if (cross.y < 0) vAngle = -vAngle;
                           Quaternion quat = Quaternion.AngleAxis(vAngle, Vector3.right);
                           _mainCamera.transform.rotation = Quaternion.Euler((quat * _mainCamera.transform.rotation.eulerAngles));

//1-й
mainCamera.transform.rotation = Quaternion.AngleAxis(angle, Vector3.right) * mainCamera.transform.rotation;

//2-й
mainCamera.transform.RotateAround(target.position, Vector3.right, -angle);

void Update()  
     {
         if (Input.GetMouseButtonDown(0))
         {  
         }
     }

BitStream bitStream = new BitStream(isTypeSafe);
         bitStream.WriteByte(species);
         bitStream.WriteInt32(revision);
PlayerPrefs.SetString(species.ToString(), bitStream.ToString());

BitStream bitStream = new BitStream(isTypeSafe);
bitStream.WriteString(PlayerPrefs.GetString(species.ToString()));
species = bitStream.ReadByte();
revision = bitStream.ReadInt32();