Hi Loopy,
We actually use the same shape down to 12lbs in our Master Line and Premier Line bowling balls. We change the densities to create the desired total weight while maintaining as much performance as possible.
In the 13lb Gravity the RG is 2.63, the Diff is 0.039 and the Split is 0.025.
Hope this helps you out.
Since we aren't able to get on here as much as we'd like, always feel free to email us at tech@stormbowling.com with any questions.
Thanks
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Bowl up a STORM!!!!!
Storm Tech Dept
tech@stormbowling.com
Edited on 7/28/2008 4:17 PM