The operators manuel on all my Rugars [3] have said use a .457 ball. It is supposed to shave a little lead when you push it in to the cylinder. Since they will tear a ragged hole with all 6 shots at 25 yds , that has to be pretty close. If you strive for accuracy I will give you some tips, do use a ball size that shaves just a bit of lead, use corn meal or wads to fill the cylinder so that when the ball is pressed down hard it ends up just below the end of the cylinder. Make sure it does not stick out any so it dont jam the cylinder when it turns. Lee