The Reacta Shine has a grit rating of 1500 meaning it has some abrasive in it.  I was advised that the RS is better for use on lower grit balls like 1000 grit and below, while the MS works better on higher grit balls.  If you used RS on a higher grit ball, it could actually take the grit down a tiny bit.  Refer to my thread here:  

http://www.ballreviews.com/Forum/Replies.asp?TopicID=139513&ForumID=16&CategoryID=5
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Bowling Since March 2006 - "Get coaching, don't worry about it"...blah blah balh...Just answer the questions please

Arsenal:
Track Mean Machine
Hammer Black Widow
Track Equation
Track Heat Blast
Storm Spare Ball