I no not dispute this, but I wonder why it would be true? If the velocity is the same, the trajectory of the larger round ball will be better. This is because the air resistance of the ball increases with the square of the radius, and the mass of the ball increases with the cube of the radius. That means, counter-intuitively, that the BC of a round ball increases as the ball gets bigger. So, are the larger bore guns fired at a lower velocity because of intolerable recoil?