I third the GP2. I own one and it pretty much sits in my closet collecting dust because I can not find a house in my area that has enough oil for this ball to work on. I pretty consider my Delta 1 for my Heavy Oil ball on house shots
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The question isn't why do I throw all Track, it's why don't you.
Arsenal includes:
Rule GP2, Rule Delta 1, Heat Blast, Triton Heat, Desert Heat, Blue Enforcer, Sugar Ray Leonard Boxing Glove