so as long as the ball is approved and has all the other identifying marks to be legal then you can use it regardless of size.
from USBC...
"Physical Specifications" on page I-2 of the Equipment Specifications Manual, are manufacturing specifications. Meaning that all the bowling balls when submitted at the time of approval must meet those specifications. Specifications are on the initial manufactured ball and there is not a rule or specification on the size of the bowling ball during league or tournament play.
Thank you for your support and interest in the equipment specifications. If you have any other questions, please feel free to respond.
Nicki Mours
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16-17 mph,350 rpm,PAP 5 1/2 x 3/8up, HighGame 300 x 3, High Series 782
Book Average 205,PBA Xperience ave180