Actually the bombs were the same shape as depth charges, i.e. shaped like a drum.
http://en.wikipedia.org/wiki/Image
uxford_UK_Feb2005_bouncingbomb.JPG
http://en.wikipedia.org/wiki/Operation_Chastise
Be sure to scoll down the page to the 'Complete List of Aircraft Involved', and see how many of the bombs hit the target with no effect.