Re: bat speed..
Not only the weight, but also the balance point of a bat is critical. Different balance points in bats will effect the "swing" weight of a bat (See below). I would also add that any mechanical faults in the swing will be more pronounced as you add weight to the bat.
I personally, have not seen very many 13 year olds that were ready for a -3 bat. Adjusting from 60 foot bases to 90 foot bases is a big adjustment in itself, not to mention the outfield size and pitching distance.
My son is going into HS this year. He has been working with -9 to -5 bats for the last 2 years. He has been working into a V12 -3 bat for the last couple months. The V12 is weighted in the handle and swings really nice. He is hitting it harder then he ever has. However, we have always really concentrated on his mechanics. Thank you Batspeed.com!
My advice.....don't rush him into the -3. Give him time to adjust to the field size and the bat size. Get his mechanics right and the transition will be easy for him when it's time.
Moment-of-Inertia of a Baseball or Softball Bat
Swing Weights of Baseball and Softball Bats
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