Watch them bowl, if they drop the shoulder, seem to be muscling the ball, and/or cannot get the ball out on the lane, it is probably too heavy. Another test is to have them hold the ball at their side and flex the wrist, if they cannot do this without using the whole arm, the ball is probably too heavy.
There are other ways, but I am blanking right now.
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USBC Bronze Coach "I cannot change the direction of the wind but I can adjust my sails to reach my destination." Jimmy Dean
Quaker 10/93 - 4/07
Quaker