/// \param index should lie in the range 0 <= \c index <= 3.
Bullet & temp_bullet(size_type index);
Bullet const & temp_bullet(size_type index) const;
/// \param index should lie in the range 0 <= \c index <= 3.
Bullet & temp_bullet(size_type index);
Bullet const & temp_bullet(size_type index) const;