This discussion is, as usual in these types of discussions, misleading. Of course the coverstock is the most important factor in how the ball moves. However, most companies have coverstocks designed to handle certain types of oil -- i.e., more aggressive to less aggressive coverstocks. If you have two of the same ball, a tweak in the coverstock will change the ball, but the base coverstock remains the same, meaning what you are doing is not changing the amount of movement but rather, when the ball hooks. Changes in drill pattern change the shape of the hook. I find greater differences between two of the same type of ball when one is drilled say 4.5x2 and the other 4.5x5.5 than in two balls of the same type with similar drill patterns and but having a one or two level (say 1200 to 800 grit smooth) change in the finish on the coverstock.
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