Few years ago Albert Belle was caught with a corked bat, in fact, I think the rumor was that all his bats were corked. All things remaining equal, if you can swing the corked bat 1% faster you get, in theory, 1% more distance. But the bat is lighter, bat velocity has to increase by twice that of mass to get that effect. Also, because the bat's center of gravity is shifted to the outside, the sweet spot is (again in theory) bigger.

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