when looking at a hitter which plays a larger role in the distance of a hit ball (force) 1. velocity of the swing or 2. mass of the bat
taking into account the change in mass of the bat will only be an ounce either way and the change in velocity using a one ounce heavier bat will be very small also. My understanding of physics would say that the force generated would be more greatly impacted by a one ounce difference since the weight is less than half the other variable in the equation (velocity).