The original question was "Why a wad?" The answer could only be convenience, quicker to load and less mess. The only drawback is it takes up space in the cylinder. If you want to get in the max amount of powder, the wad takes up valuable space.
Black Powder: Not because it is easy, but because it is hard, because that goal will serve to organize and measure the best of our energies and skills, because that challenge is one that we are willing to accept, one we are unwilling to postpone, and one which we intend to win...